'ill \o MW;8W:i!!»?pi!lin MtUdKI Nil' MOTORCYCLE ! E E B¥ OCEE RITCH h .FIND 2. FIX 3. WHAT'S WRON FAST! SAVE MONEY! oke Engines • Four-Stroke Engines • Transmissions • Electrical Systems • Frame • Suspension Digitized by the Internet Archive in 2012 http://archive.org/details/chiltonsmotorcycOOritc H, S|ftMQJLQMGERT.-iE 10P BRA G COUNTY CHILTONS MOTORCYCLE GUIDE 629127 RITCH. 17 DATE DUE 1 APR 15 IS 193 • DEMCO 38-297 .12 7 CLASSIFICATION 17 COPY VOL. NEWPORT WAY NOV 1968 KING COUNTY LIBRARY SYSTEM COST Chilton's MOTORCYCLE TROUBLESHOOTING GUIDE OCee Ritch ILLUSTRATED CHILTON BOOKS A Division of Chilton Company Publishers Philadelphia and New York © 1966 by OCee Ritch. Published in Philadelphia by Company, and simultaneously in Toronto, Canada, by Ambassador Books, Ltd. All rights reserved. Manufactured in the Copyright Chilton United States of America. Library of Congress Catalog Card No. 66-27619 Second Printing, January 1967 Contents 1. THE FOUR-STROKE ENGINE Starting procedures The engine won't The engine is Battery 1 start 40 Alternator 42 Rectifiers 44 1 hard to start or runs 5 erratically Engine dies when throttle opened 6 Misfires on acceleration 7 Misfires under load Misfires at high 40 tips Regulator Energy transfer 46 Points and plugs 47 Coil 48 8 RPM 9 4. CLUTCH AND TRANSMISSION Poor low speed performance 10 Poor high speed performance 10 Clutch slippage Poor general performance 11 Gear grinding 53 Overheating 11 Transmissions 55 58 12 Jumping out of gear Other engine problems 12 Won't Vibration and noises 14 Jumping out Miscellaneous carburetor problems 58 shift of gear Slipping kick starter 2. 58 59 THE TWO-STROKE ENGINE 5. Starting procedure 17 CARBURETORS AND TUNING General carburetor troubleshooting 61 23 Amal 63 Engine dies when throttle opened 24 Bing Misfires on acceleration 25 Dell Misfires under load 26 Jikov Misfires at high speed 27 Keihin Poor low speed performance 27 Keihin-Honda Poor high speed performance 27 Mikuni The engine is hard to start or runs erratically 68 69 Orto 69 71 C/V 74 80 Poor general performance 28 Linkert-Schebler 84 Overheating and seizing 30 Zenith 85 Vibration 30 Tuning 86 Noises 31 Tuning specifications 87 The Oil 32 oilers pump operation 33 6. 3. 49 FRAME AND RUNNING GEAR Abnormal ELECTRICAL SYSTEMS Magneto 37 Brakes DC 39 Chain generator tire wear Wheels and suspension 91 91 93 tips 93 Chapter 1 The Four -Stroke Engine The commonest complaint or trouble encounby the motorcyclist is that the machine will not start. The reason can be extremely simple or it can be more complicated, but the basic procedure for determining what the cause of non-starting is and how it can be corrected should be followed in order to save time and to cover all the possibilities. By following an outline, the troubleshooter can also mentally or visually eliminate some steps and begin his trouble search at any point in the sequence knowing that he will not tered have to back-track. Non-starting is extremely frustrating in view of the fact that severe it is physical generally accompanied by exertion. Pumping a some kick-start on a big-displacement bike adds to the rider's indignation and the most common reaction is to lever guess hurriedly at which usually leads of the project. The the cause of malfunction to disgust first rule is and abandonment to go step-by-step should at least run. Therefore the first step in starting a balky bike is to be absolutely sure you are following the correct starting procedure. This may seem like worthless advice to the owner who has been riding a given cycle for some time, but if you are at all unfamiliar with a bike engine it is easy to apply the wrong technique and get results only part of the time. it STARTING PROCEDURES Question: is Is the fuel tap really any doubt about fuel "Reserve." On many level, "On"? If there turn the tap to two With a British bikes there are one for regular and one for reserve. double-ended push-tap, the hex end controls the reserve. If you aren't sure, before making any starting attempts, remove the line at the tap and taps, @ the switch in #1 position. (2) Vs of the total travel —about (if fitted) Open and observe fuel flow. With a supply of fuel assured to carburetor, depress the float tickler (on Amal type carburetors) until gas appears and close the air slide or close the choke. On some older Triumphs, the S.U. (automobile type) carburetor has a lever at the spark control to about one-half of full advance. British singles with starter lever down compression release, until the piston felt is On push the coming compression to compression, then operate the lease throttle slightly set re- and follow through gently on the pedal to get the piston past compression. This is a couple Kick the engine over briskly, getting all of your weight onto the lever and straightening your leg at the same time. Note: Resist the temptation to open the throttle wide at the first cough of the engine. of inches of pedal travel, generally. and methodically eliminate possible causes. Like any four-stroke-cycle engine the motorcycle's powerplant obeys certain laws. The first law is that there must be fuel and air in the proper proportion. The second is that there must be spark at the proper time. If these two are present, combustion must take place. The motor may not run long, smoothly, quietly or with good power, but bottom which is to be pulled up for starting and pushed back down when the engine warms up. In any event, richen the mixture for starting in the applicable way. Kick the engine over a couple of times with switch off and throttle open. (This should also be done in cold weather on cycles equipped with electric starter.) Hondas with electric starters can be turned over with the starter a few times with (3) THE ENGINE WON'T START Assuming that repeated applications of the foot nothing but sweat on your brow, it is time to look for malfunctions. Check the choke and throttle controls first. Is the key really on? Twiddle the key in the to the pedal resulted in switch a bit. Be sure indicator lights are on or try the horn in an effort to determine electrical current is present if the necessary somewhere in the system. // there is an obvious supply of electricity: re-check the fuel supply. Switch to reserve. Turn switch to emergency start position and try again. If there is a smell of raw gas, or visual evidence of flooding such as fuel on the carburetor, open the throttle wide and kick the starter or operate the electric starter to turn the engine over several times and thus clear out the excess fuel. If the bike doesn't start now, further checks are necessary in the fuel supply, for which see below. // indicator lights or other accessories do not function: suspect bad connections, blown fuse or bad battery. For example: even though some Hondas have an AC magneto system a discharged battery in the circuit can make the bike hard to start and poor running. Check the fuses in any model; also check all electrical connections The Four-Stroke Engine Exploded view of the 1961-1963 Norton Twin. for cleanliness tery ground. will and This tightness, particularly the batis highly critical. (The fuses vary in location but will always be close to the battery.) If fuses look good and connections seem order, check the battery. in briefly, just enough to get a flash. is strong and a good spark examine the terminals, removing, cleaning and replacing if in doubt as to their ability to pass // the battery results, electricity. The following advice // the battery responds weakly or not at all technique, either have it makers and it is admittedly not good practice, but you can satisfy yourself that there is juice (or not) by striking a quick arc charged, switch to emergency starting position (if available) or push the bike. If a dead battery is across the battery terminals with a piece of wire the sole problem, most cycles will push start fairly will scandalize battery or the handles of a pair of pliers. Do this very to the easily. direct-short Cold weather and a big bike may make the The Engine Won't Start process a bit difficult physically, but the generating all models is designed to put out power system on at low RPM, which so this helpful feature is not present in the automobile system works for you. CAUTION: If on the section you have the battery charged, read ELECTRICAL SYSTEMS book before rushing down in this to the nearest service station. If after taking this precaution the engine still won't catch, it is time to check for a spark at the plug. (We will use the singular to save words. If your model has more than one cylinder, mentally substitute the Remove word plugs.) the plug and examine the tip. If it is wet or clogged with carbon deposits, this can be the problem. Replace it with the spare you always carry in the tool kit. Second choice is to clean it. Or, // plug appears to be good, leave it conit on the head, making sure it is nected and place A grounded; then kick the starter briskly. fat, blue spark should leap between the electrodes. If the spark is a bit weak, check the gap against specifications, since Here is it may be too wide. a trick which will often get the machine running until you can get a new plug: Close the gap right up to .010" or so and re-install it. It may be breaking down under pressure in the cylinder and the smaller gap will permit it When bike won't start that fuel preliminary is present step is tank. to make sure in to function temporarily. are sure the grounding of the plug you don't have a feeler gage, an ordinary paper matchbook cover is just under .010" thick. Make the electrode gap a slip fit for a matchbook cover and it will be close enough to play jazz, as we used to say in the music business. // there is no spark at the electrodes and you that the high tension lead If is (plug wire) good and is firmly each end, you've got ignition troubles. Now, this may be a bad coil or other problems which are better covered in the ELECTRICAL SYSTEMS section of this book. Just to satisfy yourself whether the system is functioning or not, grasp the plug in one hand and push the starter lever down politely. (Don't jump on it or your eyes are liable to light up like a pinball game.) You'll feel a tingle if the ignition system is developing output. If you get no indication of electrical energy, you've isolated the problem. // the spark plug is good and you get a blue spark, there is a bare possibility that the timing is so far off the bike won't start. But chances are connected the trouble at is somewhere in the fuel system. Check the timing as a precaution, then turn the fuel tap off and remove the fuel line from the tank. Then, holding a rag or a container under the opening, turn the tap back on and observe fuel flow, if any. You can also observe whether you really have gas in the tank or some other liquid, such as water. Also, if the bike has been in storage for some decomposed to such an won't burn. The highly volatile elements that make for quick starting in a fuel blend vaporize readily. This makes old gas equal bad gas. It generally has a strong, pungent odor as opposed to the keen, light smell of fresh fuel. Water, of course, balls up in little droplets on time, the gas can have extent that Be sure that fuel tap is in correct position. it The Four-Stroke Engine First: close the fuel tap at the tank and replace the line. On Amal type carburetors, unscrew the bottom nut using another wrench to hold the larger nut above and prevent its turning. Note: The larger nut is the jet retaining nut and it is against a red fiber washer. If washer must be replaced because leaks, so don't it invariably move it. amount and Observe the which flows out needle valve loosened, the is character of the fuel any). If there is no fuel, the stuck closed. Tap on the car- (if buretor float bowl and If there is fuel, the tap and see if it will free up. or water, or a mixture, turn on gas flows through the carbure- tor in a steady quantity as it should. This to flush out the needle valve seating On is good anyway. the Keihin carburetor, such as is used on flip the wire retainer down and remove the float bowl bottom. Late models have a carburetor bowl drain screw. A twist of the screw will reveal the presence and character of the larger Hondas, fuel. At this point you have proven that there is spark at the plug and fuel at the carburetor. So, the only reason the engine won't fire must be mechanical. Before we go farther, and before you put the plug back in the hole, take a pencil, pen or other slender, long object opening until it rests and push it in the spark plug on the piston. Then push the times to be Jiggle the ignition switch and rotate it a few start sure of making contact. Some models have emergency position on switch. the rag while gas soaks right through. bottom in a container. Water also How does Condensation can account sinks to the water get into fuel? for some. Who knows how the large quantities we sometimes find can be accounted for? Not me, but there they are. stops, you // fuel flows for a moment, then have a plugged vent. Remove the filler cap and the flow should begin again. If so, unplug the tank vent, whether it is in the cap or in the tank. On Honda 250 and 305 models, the cork gasket has been known to plug the vent hole. It is some- times necessary to cap drill another vent hole in the liner. // fuel flows freely, or if it is obviously dirty, rusty or full of sediment, there will be trouble farther along the line. So, remove the fuel line at the carburetor, take out the wire gauze strainer if so equipped, and clean it. At this point, if there is fuel at the carburetor and the plug was good and not wet on examina- at the banjo, tion, try heavy choking. Then, if really working. the carburetor lightly. Make it sure the choke is doesn't start, get into Battery, fuses and rectifier are located under the cover on right side on the Honda 90. The Engine Hard To Is Start light is small enough to slip through the spark plug hole and illuminate the interior of the cylinder a feat which is not possible with any other source of light. you want to rotate the engine to bring the up for a closer look, don't use the starter. Put the transmission in top gear and revolve the rear wheel slowly. All of this can bring you to two conclusions: (7) somewhere along the line electrical or ignition problems beyond the scope of this chapter were If piston discovered. @ The engine is sick. THE ENGINE IS HARD TO START— OR RUNS ERRATICALLY Twelve volt battery fitted is Hondas. Access is 160 and larger hand cover. to model basic assumption here is that we are not dealing with a tired engine, one which is crumbling into ruin or held together with wire The via right just If such is the case, it should be hard Rather we assume that the bike is in normally good operating condition and that (?) it either becomes hard to start and runs erratically suddenly, or the condition has been getting progressively worse for some time. Check the electrical system In either case: paying particular attention to the battery if it and hope. kick start lever ment of the down pencil. slowly and observe the moveIt should If not, the clutch is slipping ing is move up and down. and all of your kick- for naught. With the plug removed an opportune time to take a compression check. (If you don't have a compression gage, you are at a point where a visit to your friendly motorcycle shop is required anyway.) This is a tricky operation for one man, unless he has the proper long-tube gage (or it is three arms), but the requirements are as follows: @ is Remove spark plug from second cylinder a twin ... to prevent accidental chat. @ @ Open throttle fully runaway against the if it at full stop. Depress starter vigorously three or four times while holding compression gage firmly in plug to start. @ — All connections, it must is a part of the system. be stressed, have to be clean and tight. In the Honda system a low-charge battery makes for a poor running engine, so suspect it first. It is easy to leave the ignition or lights on and the battery is quickly discharged to a low state. Check the spark plug for type and condition. Perhaps the wrong heat range is being used, or another engine condition can be diagnosed by @ bore. // compression is low, suspect a bent or burned valve or poor valve seating. If it is nil, or extremely low, a holed piston is probably the cause of your trouble. "Low" is a relative term, to be sure, but the average four-stroke engine should operate after a fashion on 80 psi com- pression. For verification remove the rocker box cover, or gain access to the valve clearance position as required, A adjusting and check the valve clear- very loose valve is probably bent; a very tight valve is probably burned. Before you panic, adjust the valves to proper ance. clearances and try to get the engine to run. Poor adjustment can prevent an engine from starting. (See TUNING, P. 86.) Likewise, if compression is quite low and you want to be sure that things are as bad as they seem before you pull the cylinder you can use a small bayonet bulb, such as those fitted as instrument or indicator lights, to help out. Take the bulb, solder a wire to the tip, another to the brass base and connect the two wires to a battery. This Hold spark kick starter plug against head to make good ground and lever to check for faulty ignition or bad plug. The Four-Stroke Engine Dress them or replace (preferably) If the breaker point area is oily, pitted or oily. with a new set. somewhere there Replace (On and a bad is straight magneto models, inspect the pickup and grease and correct the slip ring for dirt condition © necessary.) if engine kicks back on starting, chances If the are the automatic advance tributor If the drive. seal in oil it. © © is Check it is mechanism in the dis- not working properly. the air filter. Remove and ancient and excessively dirty, get a A clean new it. one. clogged muffler can cause hard starting. high-mileage job or is an oiler, If the bike is a suspect this cause right away. If the diffuser is removable, clean it. If the machine has been stored and has been put into use without proper attention to preparation, the carburetor idle jet can be clogged with varnish or gum residue. The main jet can likewise be plugged with this substance. Acetone is a good solvent, or regular carburetor cleaner such as that used in motorcycle shops can be used. © Open fuel tap and check quality of fuel as it flows onto rag or into container. ENGINE DIES IS WHEN THROTTLE OPENED This condition appears to cause some concern it can be due to engine problems, the most common reason for such performance is that the throttle is opened too widely too suddenly. to beginning riders and, while But, assuming that you are not being overly quick with the twist grip, this sort of death or slump of the engine can be attributed almost wholly to carburetion. © Make operating to supposed © sure that the choke lever open the choke examining the plug. See the TUNING section for details on plug type and analysis. Check the carburetor idle mixture screw. This often becomes maladjusted because the owner doesn't watch what his hands are doing © is actually when Is the idling speed set Gasoline flowing! the main Gasoline line flowing^ """the "RES" line Main line i © is the case a Replace which © it if more likely suspect is Screen the capaci- points are burned and discolored, is a good sign of a faulty condenser. This brings us to bad points: worn, dirty, If you have the engine ticking over at 200 RPM, it just can't induce enough pressure drop at the jet to suck up enough fuel. if wrong. This cause of hard starting and erratic running is gradual in its onset, rather than sudden, because it is due to the wear of the cam fiber which causes a variation in point gap. So, if sudden hard start- ing is high enough to ac- increase in venturi area? while gripping a screwdriver. Check ignition timing and correct tor. it to. commodate a sudden Small vent hole in Honda gas cap can become plugged and cause difficult starting or poor running, especially at high speed. fully Strainer cap To the wrburetor. SBSKBSE9 Operation of Honda fuel tap and filter-trap. Misfires on Acceleration ADJUSTER CLICK SRINC AIR CAP VALVE GUIDE AIR VALVE SPRING TOP AIR VALVE THROTTLE SPRING JET NEEDLE CLIP BLOCK BANJO BOLT BANJO THROTTLE Fl SLIDE LTER FLOAT NEEDLE SEATING JET NEEDLE AIR SCREW FLOAT NEEDLE JMR FILTER CONNECTION 'O RING LOC ATING PEG FLOAT SPINDLE BUSH THROTTLE^ STOP SCREW PILOT JET ^COVER SCREW „ PILOT JET COVER NUT FLOAT HOLDER MAIN CHAMBER COVER MAIN JET COVER GASKET FLOAT JET MIXING CHAMBER MAIN JET NEEDLE JET COVER NUT Exploded view of Amal Monobloc carburetor. © (T) rich. How about the idle jet? Is it clogged? The whole carburetion system can be too See TUNING last-resort suspect for this condition, but uncommon section for setting idle speeds MISFIRES and mixtures. © but it can happen: An air leak at the carburetor flange which has been compensated for by jetting and lets the engine run, but reduces the vacuum. Squirt gas from an oil can around the attaching point and note whether the engine speeds up. This is a kind of This isn't likely it is not in event of the following: ON ACCELERATION A: From low speed dropping shots under accelerabut running satisfactorily otherwise, the odds are that carburetion is the If the engine is tion just off the line, villain. The Four-Stroke Engine 8 RPM. On battery systems the ignition out of time. may be Over-richness can also be causing "eight cycling." C: At a given throttle opening, regardless of RPM If the dropping occurs at a certain point in the Rs being turned by the engine, this is poor carburetor tuning or a bad needle, perhaps one which is nicked or damaged. throttle sector regardless of the D: At no consistent or RPM Inconsistent misfiring Bottom carburetor fitted to bigger Hondas removed by flipping wire retainer at side. of can be throttle is opening ordinarily due to mal- functioning in the electrical system. Go over the bike from stem to stern sparing nothing from your rigorous scrutiny. Plugs, points, connections, The first thing to examine is the idle mixture. The classic symptom of too-rich low speed mixThis is misfiring on application of throttle. accompanied by a lumpy idle. Be sure the enriching for low speed is not overdone. Check the exhaust for black smoke, etc. Don't overlook the fact that there can be water in the carburetor float bowl which is sucked up at the start before the fuel can be replaced. Water can also be present in the mesh strainer and ture is on some models. trap A clogged can cause misfiring, but it will generally also show up as poor performance throughout the range, too. A bad spark plug, where the ceramic portion is dirty and causing flash-over, can also be responsiair cleaner ble for this occurrence. being fed into a system to go and a dirty plug it is high tension lead battery — the whole to the spark responsible. collectively plug, capacitor, works can be individually or The important point is example, on some British bikes a bad connection at the headlight shell or ammeter can cause the engine to misfire or quit because it is a link in the system! to overlook nothing. For MISFIRES UNDER LOAD This heading is meant to describe a condition something like this: You are riding along serenely and approach a hill. You open the throttle and Where high voltage is chooses the easiest way an open invitation to a direct-to-ground short. B: At a given RPM in any gear the misfiring occurs at a given RPM, no matter what gear you are using and no matter If what the throttle opening, suspect the automatic spark advance mechanism in AC magneto systems. This can be going out of phase at certain Checking compression using special tube-fitted gage. Using feeler gage to check valve clearance on Triumph. Misfires at RPM High you mount the slope with the engine putting its best efforts, it begins to drop a few beats. Gearing down, or returning to level road clears up as out the misfiring. First diagnosis of this condition is that the plug breaking down from overheating. The wrong plug is being used or gap is wrong. Second choice would be, again, dirty air is cleaner. Too main large a jet, with insufficient pressure opening and relatively low Tuning is speed, results in improper mixture. drop at wide throttle indicated. Poor fuel can play a big role in this sort of performance. Premium fuel, as recommended by the manufacturers, should be used at all times. "Cheap" gas is poor economy. Improper timing would be about the fifth item in line to be considered. Spark timing becomes more load increases. Finally, and not to be overlooked: Is the gear being used too high for the conditions encritical as the Examine snap connectors volved. countered? at all points for corrosion and looseness. Before going into them, it is first wise to is not responsible. Some establish that valve float MISFIRES AT HIGH Dropping because so at high Rs many is RPM sometimes mystifying facets of engine tuning are in- up past the redline and never realize that the valves are crashing. And, the modern engine is so sturdy that it can riders twist their engines right take a certain amount without these people never learn — disintegrating, so until too late. At over- rev peaks valves are hurled off their seats at such acceleration rates that the return springs cannot them and they open too long, then has turned past the ramp. The prolonged opening period destroys critical valve timing and causes a dilution of the fuel charge and thus the misfiring. If this isn't the cause, then you have a wide choice of possible other causes. (T) Since the main jet, without being influenced much by the needle, is responsible for mixture control at high speed, it should be looked into control crash first down off. after the stay cam Follow the specifications in fitting this important component ... or adjust according to tuning information supplied in other parts of this book. (2) Believe it or not, that old dirty air cleaner crops up again in this situation. Check it. (3) Improper float level is a common cause of high speed misfire. Set too low, the float does not permit sufficient fuel to accumulate in the bowl to serve the needs of the carburetor. dirty, wrong heat range, im(7) Spark plug: Using small light bulb to view inside cylinder through plug hole. Bulb, soldered to wire, is about to be inserted. proper gap, faulty. Any or all of these plug faults can be responsible. High pressure breakdown of a seemingly good plug can also be the trouble. Heat range is pretty critical in air cooled engines. If the plug is too cold it shorts out, if too hot it welds. If the gap is too great the cylinder pressure prevents the arc from forming across the expanse between the electrodes. Bad capacitor. Especially on the AC mag- @ 10 The Four-Stroke Engine neto system, a poor capacitor can perform satisfactorily at low speeds yet fail to prevent point arcing at higher Rs. Have it checked or substitute a new one if everything else is right. © Coil. Same situation as with capacitor. High tension leads leaking. Be sure the plug wire is not leaning on metal which would invite a direct ground. Rev the engine up and run (7) your fingers along the plug wire. tingle © if there An air leak in the exhaust system, the pipe joins the head, This dropping. You'll feel a leakage. is is also where cause high speed will accompanied by "banging in the silencer" as our British cousins say. © Air leaks possibility. at the carburetor another unTHROTTLE IS ENGINE DIES WHEN der OPENED. Late model Hondas have drain screw at bottom of carburetor for checking fuel. @ (u) at © burned or bent valve. Improper valve clearance. These two items Slightly can cause high speed misfire, but they should also make their presence felt in other ways, so this symptom (misfire) should be considered as addi- BEARING BOB WEIGHT CAM are Follow recommendations evidence leading to a conviction, rather than a definitive single issue. Clogged or restricted exhaust should always be suspected if bike is older or has had poor maintenance. been overlooked somehow, (13) In case it has check the choke. Be sure it isn't being put into tional @ CENTRAL FIXING BOLT operation. POOR LOW SPEED PERFORMANCE BEARING BOB WEIGHT Automatic advance unit (Lucas) systems using typical of most ignition coil. This symptom is presumed to be apparent as stumbling or lack of power at low Rs which clears out in the upper range of the engine. This is not to be mistaken, of course, for the loadingup which occurs at prolonged idle and which disappears as soon as excess fuel and carbon are blown out, but rather a consistent lack of per- formance bottom half of the power curve. in the Number one trouble-causer in this situation improper carburetion: Wrong idle is adjustment, the answer. wrong needle setting, etc. Tuning is Second, and not too far behind in frequency, Between these two, is improper spark advance. you'll find the trouble in most cases. POOR HIGH SPEED PERFORMANCE Complaints here are a lack of power at what should be the peak torque of the engine, reduced top speed and the need to shift down more frequently. Actually, in most cases, the rider just doesn't notice Examine breaker points for condition when hard or erratic running is the symptom. starting it but there is a general lack of power throughout the range of the engine. It is only that it becomes most noticeable when more However, if it is clearly is asked of the engine. 11 Overheating only the top end: Again, wrong carburetion adjustment is the prime suspect. This Dirty, clogged or bad air cleaner. condition can be borderline, permitting enough air flow to take care of low speed operation but causing an over-rich condition at full demand. Ignition timing and cleanliness of ignition system play a big part in top-end performance. Spark plug and wiring. See MISFIRES AT HIGH RPM (above) The engine can drop off in for more details. power yet apparently be hitting on every power stroke. How circuit of if it which the Weak Don't overlook this intended to complete a the battery? is system link in the is ignition is a part. On an older cycle or condition can prevail with this sort of result. Usually accompanied by some misfiring, however. Lack of compression. Poor mechanical condition with worn rings, valves in need of grinding and so on shows up first as lack of top end performance. Is the rider too heavy for the machine? Maybe the load capacity is being exceeded. A 300 pounder on a 50 cc. Honda can't expect blazing performance. Could be. See (9) Is it a slipping clutch? one which valve springs. is somewhat tired, this CLUTCH AND TRANSMISSION @ section. Tire pressure check. Low tires cause increased rolling resistance which is noticeable, particularly on small displacement cycles. @ Partially plugged tank vent. Carburetor mounting gaskets which can cause trouble via air leakage. engine. Slipping clutch. This should be an obvious condition to even a novice rider, but a surprising number of people don't notice it. Improper valve adjustment, burnt or bent valves can reduce horsepower. Check these items out as directed under START. THE ENGINE WONT Tired. Poor compression is the clue to the mechanically-ailing engine. Without good compression you can't have good performance. Is the sump loaded with Too much oil an engine down oil, by any chance? collecting in the crankcase will slow considerably. POOR GENERAL PERFORMANCE OVERHEATING Under this heading, naturally, can be lumped any single cause or combination of causes conceivably connected with the engine and for that matter other portions of the bike. But let's run through the most common causes, in order The air-cooled engine is designed to be cooled by a moving stream of air. This means that the machine must be moving to insure that the designer's aims are carried out. Oh, sure, your motor will sit there and bang away without complaint for several minutes, but it isn't a good idea . . . of their frequency. First suspicion should fall timing. If it is off the performance. Spark plug. engine is ignition to prolong just hopeless in at a standstill. on the this Improper type, fouled, dirty, etc. Poor carburetion. Symptoms of over-richness or too-lean a mixture are easy to detect by examination TUNING Is of plug and exhaust pipe. See (P. 86) for clues. the bike running free? is idling, or the operating while the bike So don't expect "overheating" it to be happy. complaint, all is If that's needed is a change of habit. However, if the engine overheats under normal riding conditions that is, it begins to lose power, misfires or starts to seize up, then you must assume that there is a malfunction or a poor operat- — ing condition. Check Too the rear wheel as the machine sits on the stand. Does it turn over easily? Is the brake dragging? Are wheel bearings bad? Is the chain too tight? Any of these items can slow the bike so much that the tendency is to suspect a poor-performing lean a mixture for overheating is the commonest reason on the road. Next commonest reason is improper ignition Insufficient advance is the problem. Wrong heat range spark plug can also pro- timing. duce this condition. — The Four-Stroke Engine 12 Good D-rty Eorty Ignition Operotion Hot Type Plug .. All of these conditions can be dealt with in the tune-up process. If the engine is tuned properly and it still overheats, then look to one of the following: 'efnpefQiure ® Air leak between carburetor and head resulting in an excessively lean mixture, Good Oicty Cold Type Plug torly Operotion Ignition Hoc high lempe'o'u GENERAL PERFORMANCE. Graphic illustration of plug characteristics. and most This may not be enough to cause misfiring, but that could be a clue. Not free-running. See under POOR noticeable under load. © © Low oil level. The air-cooled engine is also cooled by oil. full manufacturer's recommendation supply should be carried. © A Improper A viscosity. oil required for hot weather. proper grade in the sump? oil is © © ® «=> have the capacity being exceeded? Overimmediately productive of overheating. the engine dirty? Cooling fins, particubike's Is loading higher viscosity Do you is Is rest of the motor casting generally, must dissipate the heat generated by combustion and friction. If there is a film of dirt and oil on larly, the and the dissipation surface, A Remember: retarded. is Gunk it. clean bike runs better. MISCELLANEOUS CARBURETOR PROBLEMS WHICH CAN CAUSE HARD STARTING OR POOR PERFORMANCE Dirty, choked air cleaner filter is responsible performance complaints. for many © © jet cap on many carburetors and water trap. The main as a sediment acts If the small brass spacer is left off the float support spindle on Amal Monoblocs the float will move allowing the needle valve to drop into the bowl and cause flooding. Bent needles can upset air fuel ratio. Fuel consumption will rise if needle is worn. "6"-ring gasket on Amal type carburetors can fail or be pinched on assembly and permit © © air leaking. not against head © Warped © A small amount of water retained banjo can cause prolonged © A carburetor which has been mounted flanges will and permit seal air leak. in line difficulty. filters at rigidly, instead of with flexible mounts as original- can cause fuel frothing and a mysterious ly fitted, misfiring. ® Incorrect float level should always be suspected in case of poor high speed performance. OTHER ENGINE PROBLEMS Excess oil consumption All engines use oil, even four strokers, so expect the consumption of a certain The oil will be used. externally, BSA air cleaner location. amount of lubricant. greater the clearances in the engine, the it will Even if absorb. the high-miler The through even more, naturally. is more clean leaky bike runs But there is a 13 Other Engine Problems A are burned. compression check disclose will this condition. © the Is oil being returned to supply? On dry-sump engines this is critical. Check the screen and the return line from sump. © © Check excess the sump breather. If it is plugged, be burned. oil will Bad valve guides, with excessive clearance between valve stem and guide bore, are responsible for a certain amount of If comsymptoms are burning. oil pression checks out well, but other measure stem-to-guide clearance by ap- present, plying side-to-side pressure on valve stem with spring removed. It should not rock. Lack of oil pressure —sudden symptom, it is a problem. The symptoms would have manifested themselves as This mechanical #fi *5* a isn't difficulties because, except in the rare model equipped with an oil pressure indicator, there is no visible clue to a lack of lubrication at critical points fed by the pump. instance of a .Kfl -^*" Pressure failure generally means pump failure because of accumulated debris in the check valve in the plunger type pump. This is easily cured by removing the retaining screws, spring and ball in the check valve and cleaning the seat with solvent. Rarely, on some models, does the drive break. some types, such as the small displacement with semi-pressure lubrication to the rocker box, the grooves in the cam which feed oil up to the top of the engine can become clogged with muck if the engine is neglected long enough. Remove the rocker oil feed bolt (see illustration) and start the engine. There should be a steady flow of lubricant. In Hondas, limit and consumption exceeds the norm, by if means look What use of normal? is oil all into the problem. varies so It is impossible to say. The with model, displace- much ment and condition that any given figure would be inaccurate. However, the clues to excessive oil burning are plain if you examine the spark plug and the exhaust pipe. cative of oil burning. exhaust (as opposed comes with over-rich A wet, black plug is indiA gray smoke from the black smoke which mixture) is another sign. An exhaust pipe coated with heavy, sooty deposits is another indicator. If all © fuel these are present may be one a to and accounted for there of several things wrong. Are you using the right grade of oil? If too light for conditions (either riding or engine wear) a lot of it can blow right out the exhaust pipe. Go up a grade and see if it helps. the oil is Drain and © How refill, is the compression? Worn the passage of crankcase vapors, with oil, into . 1 ...... »,i I of course. rings permit which are heavy the combustion chamber where they Schematic diagram shows circulation separate tank and dry sump system Enfield, but typical of others. is of used. lubricant This is when Royal The Four-Stroke Engine 14 Lack of oil pressure —gradual onset Again, if there is no pressure indicator, this is not something the rider would be aware of. If there is an oil pressure gage in the system and pressure begins to drop or falls off more than usual when hot, look to excessive clearances in connecting the parts supplied under pressure: rods and mains. Lack of return tank to This problem is accompanied by the symptoms of heavy exhaust smoking and other signs of overoiling since the lubricant is accumulating in the sump is instead of making its way out. The problem pump with sheared loose pump mounting, generally right in the return drive, bad check valve, failed gasket, etc. A second possibility is that the pressure has failed for some cause. In this case, pump there would be no smoking, but the symptoms of no oil pressure would be present. On BSA twin models, remove the sump plate and free up the anti-syphon ball at the bottom of the pickup by lifting or suitable instrument. it with a small screwdriver A sticking ball is a "some- times"-happening. VIBRATION OIL RETURN \ PIPE Excess vibration is broken or worn motor mounts and all mounting points should be inspected carefully. The emphasis on the last word is because a mount plate can be fractured under a bolt head and thus loose, Cutaway illustrating differences 500-650 oil in early supply. be concealed. Incorrect clutch assembly, poor timing, worn crankshaft are other possibilities, but they are fairly easy to trace since the onset would either be gradual (in the case of the crank) or following some tinkering. If the bike is new to you. a thorough inspection of all these possible causes should be carried out since vibration is usually a prelude to some sort of failure. NOISES Noises from an engine can be both annoying and meaningful. Each engine has its own particular set of normal noises and the rider should get used to them. Then when there is a variation, no matter how slight, he is alerted. Some small noises have little significance other than to denote ordinary wear and changing of clearances valve clearance, etc., but loud, heavy or sudden noises generally come as a clap of thunder before the storm, warning of heavy weather. . . JOINT WASHER . Pinging This at ' usually directly traceable to is a high-pitched, upper cylinder rattle one half engine speed and is caused by pre- BSA 500 sump details and later BSA 15 Noises Hose connections of BSA tank ignition (detonation) of the fuel charge. It occurs most noticeably on acceleration or under load and Principal is brought on by one of several things. cause is low-test fuel. Using a poor grade (low octane rating) gasoline in a high compression engine is an open invitation to this symptom. It is more than annoying; detonation is harmful Switch to high test to bearings and pistons. (premium) gasoline. If you are using high-test gasoline and get the same sound, chances are, first, that the ignition timing is too advanced. If your model is a twin, be sure that both sets of points are opening at the proper time. Worn parts here can cause a variation between the two. Another possibility is incorrect spark plug heat range, wherein the tip is overheating and acting like a glow plug in a model aircraft engine. Still another cause can be excess carbon in the combustion chamber, or, if the engine has been recently overhauled, a bit of metal may have been left around the spark plug hole in the form of a broken thread which is heating and glowing. The latter three possibles should be considered more is if Honda wet sump lubrication system (450 engine). the pinging occurs only after the engine good and hot. Clatter This is generally the description applied to ex- cessively loose valve/rocker clearances. when the engine is has warmed up and is clearly noticeable There of the engine. is in the a certain even upper part amount of valve noise in an air cooled engine, but ance more when it It is cold than if tappet clear- way through, no one valve stands out as being noisier than the others. short length of rubber tubing can be used to listen is all the A arm in turn and isolate the noisy long screwdriver with handle held to the to each rocker one. A ear and tip against the rocker same purpose. box can serve the BSA 250 oiling method— note anti-syphon sump (0 which sometimes sticks. ball valve in 16 The Four-Stroke Engine Ride the machine at low speeds under load and if the sound intensity increases as throttle is opened. see Rap Descriptive of excess clearance in connecting rod bearings in most engines, this noise is most noticeable when the engine is running under a light load decelerating. It should also increase in loudness with speed. Knock is a heavier sound than any described so and comes from the bottom region of the This Semi-pressure oiling system, as exemplified by Honda 50cc, uses splash feed in crankcase. spiral groove on camshaft to feed upper cylinder components. Clank or slap Piston slap in the air-cooled engine takes on a metallic ringing sound than it does in the water-cooled engine. So if you hear a half-speed more clank, like bringing a piston and a cylinder barrel smartly together, chances are it is piston slap caused by excessive piston-to-wall clearance. Slight noise, one that disappears after the engine is warmed up, can be tolerated, but one which hangs on should be investigated. To verify the cause, first determine if it is common to both cylinders if the engine is a twin, by removing a plug wire from each cylinder in turn. The nonfiring cylinder should not make a distinct noise. far indicating that it is a main-bearing or crankshaft problem in those engines with plain bearings. Most easily detected when under acceleration or when starting. engine, Screech or whine Since Hondas and others have ball and roller supporting the crankshaft, the heavy metallic thump of a bad plain bearing is not a symptom. Instead a screeching, whining sound, like a faulty siren or the rear end of an old Buick, occurs when bearings go bad (very rare under normal circumstances). bearings Double knock Symptomatic of excessive piston pin clearance. is most noticeable with the engine idling and is a sharp, quick double-rap. This Chapter 2 The Two -Stroke Engine Cutaway The two-stroke engine cycle so is of Suzuki twin 250cc. with an old two-stroke outboard motor, a model airplane, or a model car engine knows the frustration of trying to get exactly the right conditions basically seems there should be few causes of trouble. This is true. Like comparing an aircooled powerplant to a water-cooled one, the twostroker has much less possibility of going bad than simple that it The reduction the four-stroke type. enough parts alone is problems. But this that a two-stroke which it is to eliminate does more not potential necessarily The reliable. mean ills to subject are often just as prevalent and, is in the case of the rider, just as baffling. It is assumed knows that the reader of the two-stroke cycle principle. the essence If not, refer- ence to the accompanying chart will make the gas flow through the engine clear and that's about all there is to understand. The carburetion and ignition of the two-stroke are shared with the four. stroker and, aside tion of the together) is from . . is the things start and run. With cold engine or employed. (?) @ @ This reference to the four-stroke is made because the average rider has at least a nodding acquaintance with the "conventional" engine so widely used in automobiles. If you are used to dealing with the valve-equipped type, you will find Turn Turn in cool weather the fuel tap to the "on" position. first notch or mark. choke. (Jiggle the carburetor tickler if so equipped.) (4) Kick the starter or push the electric starter the key to the Close the button. pronounced differences in the two-cycle. If you have no experience with either type of engine, you can pick up enough hints here to make the various functions of components clear. The biggest owner complaint is either that the engine is hard to start or it won't start. Other Note: several Do not open the throttle while operating the starter, and resist the temptation to crank the on soon as the engine fires up. as the engine is running smoothly (throttle still closed), gradually begin opening the choke, and as soon as the choke can be reduced, open the throttle and speed the engine up. Gradually open the choke as engine warms up. throttle (5) away sharply in perAnyone who has fiddled gripes or troubles dwindle centage below these two. The modern STARTING PROCEDURE lubrication, the configura- modern power unit (engine/gearbox about the same whether the two- or four-stroke principle make motorcycle engine isn't nearly so finicky, but all models have their bad moments and the best procedure, for amateur and old-timer alike, is to begin with the correct starting procedure as recommended by the manufacturer. If you don't have the owner's handbook, or if the bike is strange to you, here is a procedure which will get any two-stroker going— if there is nothing wrong with it. Run through it before you assume that something is wrong with the powerplant. moving in many to two-stroke 17 as As soon 18 The Two-Stroke Engine With warm engine or in hot method of eliminating weather items. As with a four- truth in the statement that you and 2 above, leave the choke alone and open the throttle Va to lA and kick the engine over on the starter. Seems simple, doesn't it? It is, but suppose the engine doesn't fire up right away. Suppose you have a spark and you have fuel and you bring them together under pressure at the right time, you'll have an explosion. So, either you have no fuel, you have no spark, you have no compression have been kicking the or you haven't got the right time. Following 1 starter for a considerable number of times and the only sound you get is your own panting. Then what? Then you've stepped into the twilight zone where anything in the world could be wrong, but chances are that only one of a few things is likely wrong. To find out what "thing" and how to proceed, it is necessary to follow a step-by-step NEW stroke, there if Bear up and follow through on the following: // there is a smell of raw gas, or visual evidence of flooding such as fuel on the carburetor, open the throttle wide and kick the (7) starter, or operate the electric starter to turn the NEW MIXTURE BEING COMPRESSED READY FOR FIRING MIXTURE FROM CRANKCASE is VIA THE TWO TRANSFER PORTS PISTON RISING MIXTURE FROM PREVIOUS CYCLE BEING COMPRESSED PISTON RISING PISTON DESCENDING ON POWER STROKE NEW MIXTURE FROM CARBURETTER EXHAUST AND TRANSFER PORTS CLOSED MIXTURE IN CRANKCASE BEING COMPRESSED 19 Starting Procedure Example of Rotary Valve YA-5 ENGINE (ROTARY I Suclion Compression im Cylinder VALVE) DIAGRAM 2 Explosion Expression (*i Crank Ca Ex.1 Disk acts as Valve. opened Ex.2 Crank acts as valve. Operation of the rotary valve. V^_,/ Center of engine over several times and thus clear out the excess fuel. @ Is the key really on? the switch a bit. try the horn to determine cal current (3) ity, // is there Twiddle the key in lights are on or Be sure indicator if the necessary electri- somewhere in the system. an obvious supply of electric- present is re-check the fuel supply. Switch to reserve. Turn switch to emergency start position (if present on your model) and try again. If the bike doesn't start now, further checks are necessary in which see below. indicator lights or other accessories do not function, suspect bad connections, blown fuse, or bad battery. For example, even though some bikes have an AC magneto system, a discharged battery in the circuit can make the bike hard to start and result in poor running. Check the fuses in any model. The fuses will vary in location but will always be close to the battery. Also check all electrical connections for cleanliness and tightness, particularly battery ground. This is highly critical. If fuses look good and connections seem in order, check the battery. The following advice will scandalize battery makers and it is admittedly not good practice, but you can satisfy yourself that there is current (or not) by striking a quick arc across the battery terminals with a piece of wire or the handles of a pair of pliers. Do this the fuel supply, for (4) // very briefly, just enough to get a EXHAUST EXHAUST- SWEEP flash. battery is strong and a good spark results, examine the terminals, removing, cleaning, and replacing them if in doubt as to their ability // the to pass electricity. @ If the all to the battery responds iceakly or not at either have it direct-short technique, emergency starting position push the bike. If a dead battery is the sole problem, most cycles will push start fairly easily. Cold weather and a big bike may make the process a bit difficult physically, but charged, (if switch to available), or Boost Port Operation of the two-stroke cycle Third Sweep Port engine with rotary valve. 20 The Two-Stroke Engine Typical the generating system on all displacement two-stroke, small models is designed power at low RPM so this helpful feature which is not present in the automobile system works for you. CAUTION: If you have the battery charged, read the section on ELECTRICAL SYSTEMS in this book before rushing to put out down to the nearest service station. your model has more than one cylinder, mentally word plugs.) Remove the spark plug and examine the tip. can be "bridged" with a tiny sliver of metallic deposits between the electrodes; it can be fouled with heavy, wet carbon deposits; the gap can be too wide or completely closed up. Or, the plug can be internally shorted. Clean the tip, or better, replace the plug with the one you thoughtfully packed into the tool kit. If the plug appears to be good and you It @ think the keep it condition of the electrodes shouldn't from operating, replace the high tension lead, place it firmly against the fins of the engine head, and kick over the starter. You should get a fat, blue spark. If the spark is weak, check the electrode gap. In the two-stroke it should be .020" to .030". Anything above .030" is too much. Less than .020" isn't particularly critical. As a matter of work by fact, you can sometimes make a plug closing the gap right up. Set 50cc M15D. it. The plug may be down under compression and the closer .015" or so and re-install breaking gap permit it to operate until you can with a new one. will often replace it If you don't have a feeler gage, take a paper matchbook and a business card. Together they about .015" in thickness. Adjust the plug gap so that this sandwich will just slide between the electrodes and the gap will be approximately total taking this precaution the engine still won't catch, it is time to check for spark at the plug. (We will use the singular to save words. If If after substitute the Suzuki it down to correct. If there is no spark at the electrodes and you are sure the grounding of the plug is good and that the high tension lead (plug wire) is firmly connected at each end, you've got ignition This may be a bad coil, bad points, or other electrical problems which are better covered troubles. another section of in this book. Just to satisfy yourself as to whether the system is functioning or not, grasp the plug in one hand and push the starter lever down your eyes are game.) You'll politely. liable to (Don't jump on light up like it or a pinball feel a tingle if the ignition system developing output. If you get no indication of electrical energy, you've isolated the problem. If the spark plug is good and you get a blue spark, there is a bare possibility that the timing is so far off the bike won't start. But chances is ® are it is timing somewhere first in the fuel system. Check the as a precaution. To check timing (roughly), put a pencil or other slender object into the spark plug hole; put 21 Starting Procedure £^fe^ Make sure choke Is is operating properly encountered. if hard starting Has it been left on while bike was crankcase and carburetor could be full of the fuel tap on? parked? If so, fuel or oil. Jiggle it on and switch making contact? assuming the worst. Switches of this type make a circuit to ground and can sometimes be ungrounded, by removal from mounting, to cure an internal Is about fault. the key before Is there really a supply of fuel? And how old is it? is The Two-Stroke Engine 22 a fuel blend vaporize readily. This to bad gas. It generally has starting in makes old gas equal a strong, pungent odor as opposed to the keen, light smell of fresh fuel. In those models which use a fuel-oil mixture, get a lot of oil and little gas. Mixed does not separate but, in storage, the gasoline can vaporize, leaving oil or a too-rich mixture in the bottom of the tank. you might fuel/oil easily recognized because it balls up on the rag while gas soaks right in. It also sinks to the bottom in a container. If the fuel flows for a moment and then stops, remove the gas tank cap and see if it starts Water is in droplets © again. If it does, this is the symptom of a clogged vent. Depending on the model, the vent is in the cap or in the tank. Find it and unplug it. © flows freely, fuel If rusty, dirty, or if trouble farther along the line. On many models it is necessary to take the battery out to get at wiring connections. strainer at the banjo, if alive, which relates to the right cylinder, if it is a twin. some point in the stroke grossly removed from this amount of advance, then time roughly by this method or follow the points open at remove the gauze it. At this point, if there is fuel at the carburetor and the plug was good and not wet on examina- breaking open. Be sure you have the If So, so equipped, and clean have a spark at the plug right time, and the engine of points obviously there will be fuel line at the carburetor, take out the wire the gear selector in top gear and turn the engine over by rotating the rear wheel. Ascertain when the piston reaches the top of its stroke by watching the pencil. Then turn the wheel backward until the tip of the pencil is about Va" below its peak point. Then remove the breaker point cover and examine the points. The points should be just set is it or full of sediment, tion, try heavy choking. Then, if really working. Make it sure the choke is doesn't start, get into the carburetor lightly. If fuel it's is at main jet, and you approximately the still come refuses to likely you've got insufficient compression. means This present at the a broken blown gasket, leaky check it out, take sump piston, holed piston, or something big. a compression check. To The through as indicated under TUNING. If you have cleaned the plug and there is a good spark, and the ignition appears to be in time, before replacing the spark plug, kick the starter lever a couple of times, or operate the electric starter briefly. Then replace the plug and try to start the engine. If the engine fires and runs only momentarily with a big cloud of smoke from the exhaust, the chances are the sump is loaded with fuel or oil. On most models you will find a small drain plug in the center of the bottom of the sump to permit the drainage of such unwanted liquid. It may be necessary to kick the engine over a couple of times with the plug out to achieve the desired result. Then re-examine the spark plug. © Check the fuel supply. Pull the fuel line Then, holding a rag or a container under the opening, turn the tap back on and observe fuel flow, if any. You can also observe whether you really have gas in the tank or some other liquid, such as water. Also, if the bike has been in storage for some time, the gas can have decomposed to such an extent that it won't burn. off at the tap. The highly volatile elements that make for quick Tools in kit spark plug wrench to blade of Phillips screwdriver. include be used with — ) The Engine Hard To Is 23 Start average 50 cc two-stroke runs over 100 psi compression normally. If it is below 60, chances are won't run. The 80 cc, 100 cc, and 125 cc it models usually run from 115 to 125 psi normally. The 250s have about 140-150 psi. If this falls below 80 psi on the smaller bikes and 100 on the larger ones, they're in trouble, so let this be your guide. (It is difficult to find compression data on two-strokes in many of the factory service manuals, so experience and rule of thumb have to be the guide.) @ To check compression, ordinarily the ento get the most accurate reading. In the case of a non-start, however, it isn't critical. If lack of compression is the cause it will be quite low 50 per cent of normal or so. Proceed as follows: screw the compression gage end into the spark plug hole (or hold it firmly if using the automotive type), open the throttle fully and kick the starter over a couple of times. warm gine should be — Scuzzy-looking plug like this is obvious clue to no-start or hard-start problem. Replacement is better than cleaning. Of course you can have compression and none at the bottom at the top and in a two-stroke it appears to be normal in combustion pressure, suspect leaking sump seals or gaskets, other sump leakage, a sheared rotary valve pin, or that the fiber has sheared off the metal center. won't operate. engine // the run If this is a is it So, new if it fires occasionally a rotary valve model, the chances are the rotary valve disc fiber and subject is The valve defective. If illustrations of two-stroke principle) either not pression Check for spark plug, grounding plug working starter lever. at on head and is is from moisture as the valve is bad (see to distortion well as sheared drive. is but ivon'f of conditions. set drawn the mixture into the crankcase or com- destroyed. THE ENGINE IS HARD TO START- -OR RUNS ERRATICALLY The just basic assumption here is that dealing with a tired engine, we are not one which is crumbling into ruin or held together with wire and hope. If such is the case, it should be hard to start. Rather we assume that the bike is in normally good operating condition and that ( 1 it either becomes hard to start and runs erratically suddenly, or (2) the condition has been getting progressively worse for some time. In either case, check the electrical system paying particular attention to the battery if it is All connections, it a part of the ignition system. have to be clean and tight. Check the spark plug for type and condition. (J) Perhaps the wrong heat range is being used, or another engine condition can be diagnosed by examining the plug. Check the carburetor idle mixture screw. This often becomes maladjusted because the must be Breaker point location makes it in typical AC magneto easy to check condition and gap. system @ stressed, 24 The Two-Stroke Engine owner doesn't watch what his hands are doing while gripping a screwdriver. Check ignition timing and correct it if it is wrong. This cause of hard starting and erratic running is gradual in its onset, rather than sudden, because it is due to the wear of the cam fiber which causes a variation in point gap. So, if sudden hard starting is the case, a more likely suspect is the capacitor. Replace it if points are burned and discolored, which is a good sign of a faulty condenser. This brings us to bad points: worn, dirty, Dress them or (preferably) replace them with a new set. If the breaker point area is pitted, or oily. somewhere there oily, Replace drive. (On straight up and a is bad oil seal the in it. magneto models, inspect the pick- ring for dirt and grease and correct slip the condition if necessary.) engine kicks back on starting, chances are the automatic advance mechanism in the distributor is not working properly. If the Check If is it the air filter. Remove and clean ancient and excessively dirty, get a This vent, used on Yamaha and others, can get plugged. it. new one. A clogged muffler can cause hard starting. bike is a high-mileage job, suspect this cause right away. If the diffuser is removable, clean it. If the If the machine has been stored and has been put into use without proper attention to preparation, the carburetor idle jet can be clogged with varnish or oil residue. The main jet can likewise be plugged with this substance. Acetone is a good solvent, or regular carburetor cleaner such as that used in motorcycle shops can be used. ENGINE DIES IS WHEN THROTTLE OPENED Blowing through gas cap is test for venting ability. Assuming that you are not being overly quick with the twist grip, this sort of death or slump of the engine can be attributed almost wholly to carburetion. Make sure that the choke lever is actually operating to open the choke fully when it is supposed to. Is the idling commodate speed set high enough to ac- a sudden increase in venturi area? If you have the engine ticking over at 200 RPM, it just can't induce enough pressure drop at the jet to suck up enough fuel. How about the idle jet? Is it clogged? The whole carburetion system can be too rich. but it can happen: an air carburetor flange which has been compensated for by jetting, thus letting the engine This leak at isn't likely the This type of cap (neoprene liner) is almost totally immune to vent stoppage. — Misfires run, but reducing the vacuum. from Squirt gas Top an oil can around the attaching point and note whether the engine speeds up. This is a kind of last-resort suspect for this condition, but uncommon is it 25 on Acceleration Lock Screw Breaker Arm not in event of the following: MISFIRES ON ACCELERATION Governor From low speed A: If the tion just engine off is dropping shots under accelera- the line, but running satisfactorily otherwise, the odds are that carburetion is the villain. Examine the idle mixture. The symptom of too-rich low-speed mixture (T) — contact breaker points (typical) different have different adjusting methods. Layout of classic is units mis- on application of throttle. This is accompanied by a lumpy idle. Be sure the enriching for low speed is not overdone. Don't overlook the fact that there can be water in the carburetor float bowl which is sucked up at the start before the fuel can be replaced or water in the mesh strainer and trap on some matter what gear you are using and no matter what the throttle opening, suspect the automatic spark advance mechanism in AC magneto systems. This can be going out of phase at a certain RPM. On battery systems the ignition may be out of time. Over-richness can also be causing models. "four-stroking." firing @ (D A clogged air cleaner can cause misfiring, but it will generally also show up as poor performance throughout the range, too. (4) A bad spark plug, where the ceramic portion is dirty and causes flash-over, can also be responsible for this occurrence. age is way Where high volt- being fed into a system it chooses the easiest go and a dirty plug is an open invitation to to a direct-to-ground short. B: At a given If RPM the misfiring C: At a given throttle opening, regardless of RPM If the dropping occurs at a certain point in the throttle sector regardless of the Rs being turned by the engine, this is poor carburetor tuning or a bad needle, perhaps one which is nicked or damaged. D: At no consistent throttle opening in any gear occurs at a given or RPM, no RPM Inconsistent misfiring is ordinarily due to mal- functioning in the electrical system. Go over the bike from stem to stern sparing nothing from your rigorous scrutiny. Plugs, points, connections, high tension lead to the spark plug, capacitor, battery —the whole works can be tively responsible. individually or collec- The important point is to over- look nothing. Idling HH mixture adjustment on typical two-stroke carburetor. Muffler baffle can be cleaned in solvent. hard carbon it If very dirty with can be heated with a torch. 26 The Two-Stroke Engine @ @ MISFIRES UNDER LOAD Second choice would be, again, dirty air cleaner. This heading is meant to describe a condition something like this: You are riding along serenely and approach a hill. You open the throttle and as you mount the slope with the engine putting out its best efforts, it begins to drop a few beats. Gearing down, or returning to level road clears up the misfiring. @ First diagnosis of this condition is Too large a main jet, with insufficient pressure drop at wide throttle opening and relatively low speed, is results in improper mixture. Tuning indicated. @ Poor fuel can play a big role in this sort of performance. Premium fuel, as recommended by that the breaking down from overheating. The wrong plug is being used or the gap is wrong. plug is KLG assembled ignition A dirty carburetor check such as this can always be suspected. carburetor is a necessary step in fuel lack. Use solvent and plastic sprayer. Cleaning dirty type spark plug can be used to system output without fear of shock. locating Take KLG assembled type plug apart and use inner core check condition of spark output. Holding electrode near engine and operating starter should produce good spark. to 27 Poor High Speed Performance fingers along the plug wire. if Main Switch C DIES @ Spark Plug Condenser Contact Breaker Breaker the of ignition system using manufacturer, should be used Cam at all fifth jet, Improper float level is a common cause of high speed misfire. Set too low, the float does not permit sufficient fuel to accumulate in the to serve the needs of the carburetor. inder plug welds. pressure is If the prevents too cold gap the it shorts out, if too great the cylarc from forming is across the expanse between the electrodes. Bad capacitor. Especially on the AC Coil. Same bottom half of the power curve. is trouble-causer in this situation improper carburetion: wrong needle setting, etc. wrong idle adjustment, Tuning is the answer. Second, and not too far behind in frequency, improper spark advance. Between these two, you'll probably find the trouble. is POOR HIGH SPEED PERFORMANCE Complaints here are a lack of power at what should be the peak torque of the engine, reduced top speed and the need to shift down more freActually, in most cases, the rider just but there is a general lack of power throughout the range of the engine. It is only that it becomes most noticeable when more is asked of the engine. However, if it is clearly only the top end: Again, wrong carburetion adjustment is the doesn't notice it prime suspect. bad air cleaner. This concan be borderline, permitting enough air flow to take care of low speed operation but causing an over-rich condition at full demand. Ignition timing and cleanliness of ignition system play a big part in top-end performance. Spark plug and wiring. See MISFIRES AT HIGH SPEED (above) for more details. The engine can drop off in power yet apparently be hitting on every stroke. Dirty, clogged or dition mag- neto system, a poor capacitor can perform satisfactorily at low speeds yet fail to prevent point arcing at higher Rs. Have it checked or substitute a new one if everything else is right. © This symptom is presumed to be apparent as stumbling or lack of power at low Rs which clears out in the upper range of the engine. This is not to be mistaken, of course, for the loading-up which occurs at prolonged idle and which disappears as soon as excess fuel and carbon are blown out, but rather a consistent lack of performance quently. Spark plug: dirty, wrong heat range, improper gap, faulty. Any or all of these plug faults can be responsible. High pressure breakdown of a seemingly good plug can also be the trouble. Heat range is pretty critical in air cooled If the oil seal. POOR LOW SPEED PERFORMANCE Number one Believe it or not, that old dirty air cleaner crops up again in this situation. Check it. it Bad crankshaft @ in the without being influenced much by the needle, is responsible for mixture control at high speed, it should be looked into first off. Follow the specifications in fitting this important component ... or adjust according to tuning information supplied in other parts of this book. engines. OPENED. Leaking head gasket. Leaking cylinder/crankcase gasket. These three can cause too-lean a mixture and thus be responsible for misfiring. Try the same tactics as described to check for a leak at the carburetor flange. Often a new dressing of gasket compound will take care of the problem. Don't overlook the clogged muffler reminder. This condition breeds all sorts of symp- times. MISFIRES AT HIGH SPEED too hot IS another ENGINE toms. item in line to be considered. Spark timing becomes more critical as the load increases. Finally, and not to be overlooked: Is the gear being used too high for the conditions encountered? bowl (n) WHEN THROTTLE is coif. "Cheap" gas is poor economy. Improper timing would be about the Since the main You'll feel a tingle leakage. Air leak at the carburetor flange Follow clues under in gnition Coil Diagram is possibility. Secondary Primary there situation as with capacitor. High tension leads leaking. Be sure the plug wire is not leaning on metal which would invite a direct ground. Rev the engine up and run your Battery condition is important in certain 28 The Two-Stroke Engine Carburetor Cover Rubber Packing Inlet Carburetor Cover Port Heat Proof Packing Carburetor Spring Washer ®~. Carburetor Lock Bolt T5 Carburetor Set Bolt Carburetor Lock nut Carburetor Air Cleaner Collar Air Cleaner Washer SeO Cleaner Have it checked for output and complete the circuit. Poor mechanical condition: bad rings, low compression, leaking gaskets and seals, clogged ports. Borderline components reveal themselves Bolt electrical circuits. ceivably connected with the engine ability to that matter other portions of the bike. © first at © top speed. Is from the simple fact enough for the job and the bike at ® heavy for the machine? some owner complaints stem that the horsepower there's nothing isn't wrong with the tire pressures. Low increased rolling resistance but a large tires cause number of riders fail to take this into consideration. © Check (10) Possible cause could be plugged fuel tank for slipping clutch. AND TRANSMISSION vent or restricted gas See CLUTCH section. lines. POOR GENERAL PERFORMANCE Under any this heading, naturally, can be lumped single cause or . and for But let's causes, in order of © First suspicion should If it performance. Spark plug. © © fall the engine is off Improper is on the ignition just hopeless in type, fouled, dirty, etc. Poor carburetion. Symptoms of over-rich- ness or too lean a mixture are easy to detect by all. Check common . their frequency. timing. the rider too Surprisingly enough, run through the most . combination of causes con- examination TUNING © of plug and exhaust pipe. See for clues. Is the bike running free? Check the rear wheel as the machine sits on the stand. Does it turn over easily? Is the brake dragging? Are wheel bearings bad? Is the chain too tight? Any of these items can slow the bike so much that the tendency is to suspect a poor-performing engine. Slipping clutch. This should be an obvious condition to even a novice rider, but a surprising © number of people © don't notice it. Poor general condition. Under this heading 29 Poor General Performance Voltage regulator and connections are under seat of Big Bear and other models. It is Yamaha necessary to remove gear change lever on models to take off transmission side cover. some Put cellophane strip between closed points, tug gently and rotate flywheel to timing marks. Points should just open and release paper when marks coincide. Location of timing marks on Suzuki 80, typical of flywheel rotor AC magneto systems. Burned piston shows evidence Use a strip cellophane from cigarette emergency for checking timing. of package in of Lack of oil, too-lean fuel advance can produce this condition. port. vaporizing mixture, at exhaust spark wrong 30 we The Two-Stroke Engine find the low-compression causes: bad worn piston crankcase (cylinder-to-case, end seals of crankshaft), etc. And on the high-mileage model this should be obvious after a routine checkrings, up. On seals at a newer cycle, damage seals or non-seated rings to gaskets, faulty can be the problem. and especially has a tendency to "run on" is a carbon build-up which must be removed to restore performance. This is somewhat rare, but if you don't know the history of the offending engine, it is if it after the ignition, there © possible that somebody gasket and compression The air-cooled engine is away the heat generated by combustion Overloading or riding too slowly will result in a build-up of heat which, in turn, leads to piston seizure and difficulties of that nature. However, overheating under normal conditions (that is, under similar circumstances which previously did not cause overheating) is a fairly to carry and friction. common complaint. Most small of the trail variety piston seizure at some two-strokers, experience career without any real damage. Just letting the machine cool down and free itself is generally sufficient, but if the engine does not perform up to standard after such an experience, broken rings and scored cylinder walls are probably to blame. If the bike is prone to overheat, any one of several causes could be present. particularly, time © in their Incorrect fuel/oil mixture. Insufficient the mixture or the oil in wrong grade of oil can cause tank is accidentally filled with straight gas and the engine operated it will seize in a short time. Lack of oil in the automatic oiler tank or inoperative oil metering device. (See section at the end of this chapter on these devices.) overheating. wrong head Or, the head in- crease compression and performance with a consequent heat build-up the engine's fins weren't is a marvel of efficiency only human. In the motorcycle installation, without any cooling fan, the engine depends on a stream of air caused by the vehicle's motion it too high. could have been milled or the case stuffed to OVERHEATING AND SEIZING but installed the is designed to cope with. Clogged exhaust port. © @ Accompanies excess carbon in combustion chamber. Clogged exhaust pipe. Too much back pressure can cause overheating. Clean the system. clutch. (fi) Slipping This is, again, rare and seemingly impossible to overlook, but it has been known to be the basis of an owner's complaint. Chassis faults: brake dragging, bad wheel bearings, low tires, etc. all combine to place a drag on the engine. @ @ @ Overloading. This comes under the same general category as improper use. Dirty engine. The cooling fins can't dissipate much heat if they are covered with mud, dirt or grime. Not that they have to be spotless, but an excess of detritus can cause overheating. VIBRATION Excess vibration is usually directly traceable to broken or worn motor mounts and all mounting points should be inspected carefully. loose, If the © @ Fuel-air ratio wrong. Too lean a mixture is a prime cause of overheating. Set carburetor adjustment to provide richer mixture. Retarded ignition. Failure of automatic advance mechanism or incorrect static timing can be '[: @ it responsible. Entrance of Here is air into combustion mixture. the leaky gasket or oil seal bit again. Carburetor, head, cylinder/sump or crankshaft end sealing is poor. Squirting gasoline from an oil can at the junctions with the engine running is a crude test. If the engine speeds up, you've found the bad gasket without © Wrong much rViU effort. heat range spark plug. Overheating is usually just one of the symptoms when the wrong plug is used. It helps confirm the cause of and loss of power. Excess carbon deposits in combustion chamber. Take a compression check. If it is grossly high but the cycle doesn't run particularly well, *=H 1 misfiring © Connecting rod end-shake caused by worn big end bearings causes piston slap. 31 Noises £* Pure gasoline OIL TANK AUTOLUBE REGULATOR CABLE THROTTLE CABLE OIL AUTOLUBE (OIL FEEDTO INDUCTION INJECTOR) TRACT ROTARY INLET VALVE WORM DRIVE PRIMARY TRANSMISSION 6EARS Yamaha Autolube oil injection the last word is because a mount can be fractured under a bolt head and thus be concealed. Incorrect clutch assembly, poor timing, worn The emphasis on plate crankshaft are other possibilities, fairly easy to trace since the onset but they would are either be gradual (in the case of the crank) or following some tinkering. If the bike is new to you, a thorough inspection of all these possible causes should be carried out since vibration is usually a prelude to some sort of failure. NOISES Two-stroke noises are different from anything and in the case of the air-cooled engine they are even more distinct in character. Any abnormal noises are cause for investigation although they may be only the result of normal wear causing greater clearances, etc. Unusual noises can be classified in three ways: intermittent, continuous and changing according to conditions. else Intermittent noises (not always present): \. On hard acceleration, a click or clatter can be the result of a build-up of carbon deposits on the rings which destroys end clearance, or it system in schematic form. A heavier can be excessive ring land clearance. sound, but still a light mechanical sound and sometimes a double-rap is generally worn piston pins or bushings. A knock under these circumstances is ordinarily traceable to connecting rod bearings. Pinging is caused by low-test fuel, carbon build-up in combustion chamber or too much spark advance. a rattle or clank is indicative (2) At low of piston slap, or excessive clearance between piston and cylinder wall. lighter noise but strictly metallic can be the piston impinging on port openings. Check this by closing the throttle quickly and noting if the cylinder head vibrates. RPM A Changing noises Noises which change according to conditions come and go because of temperature changes. These are metallic light knocks. (7) On starting engine or when cold indi- ordinarily cates excessive piston/cylinder vanished when the engine is clearance if it hot. At high temperature if the same sound as cold but diminished somewhat, this is a sure sign of too much clearance. If the sound occurs (2) when more when hot than when connecting rod. cold, it can be a bent The Two-Stroke Engine 32 To clutch Oil chomber pump Drain plug Suzuki Posi-Force lubrication system Continuous noises A heavy thump under (2) Sharp knock (J) lip is conditions gen- descriptive of piston rings Clutch noises are often credited to the Excess clearance between clutch steel and the .:b is a fooler. The noise here ' decreases or disengaged. quits entirely when the clutch is THE OILERS As far as convenience and efficiency are concerned, the introduction of automatic oiling systems was a dramatic improvement in two-stroke motorcycles. However, these pumps and their attendant plumbing give the rider one more item and consider. The rate of failure and faulty operation has been no greater than any other oil pump system in any four-stroke motorcycle, but since many dealers and owners had never worried about such a device on a twostroke before, there have been some loud complaints when things went wrong. Two systems are used. One is exemplified by to learn about the Yamaha "Autolube." mixture behind the carburetor venturi and lubrication is accomplished in the same manner as in the conventional gas ml pre-mix method. The difference is that the amount of lubricant metered according to engine speed and load with a rich mixture of oil for high speed and a is lesser amount of oil for idling, etc. In addition system provides for lubrication with the throttle completely closed where the engine is being used as a brake on long downhill runs. The second system is typified by Suzuki's "PosiForce" method where oil is pressure-fed to the crankshaft and via drilled passages to the connecting rod and then sprayed into the fuel-air mixture in the cylinder. The amount of lubricant delivered is controlled by throttle position and engine needs. the of a port. engine. plates schematic form. fuel-air all erally stands for bad crank bearings. However, it can be a flywheel rubbing against the case because of improper shimming, causing the crank to be off center. catching on the in Oil is injected into the Accompanying illustrations will make the parts relationship clear. In the Yamaha 250 and 305 the pump is driven off the main gear (primary) and is thus operated only when the clutch is engaged. In the Suzuki, the pump takes off from a gear on the starter shaft and is in action regardless of whether the clutch is engaged or not. The only operating hazard of the Yamaha system in the 250 and 305 is that of running the engine for long periods with the clutch lever held down. This is a bad habit of some riders who wait out traffic signals with first gear engaged and the clutch thrown out. Pump Oil Oil delivery failure Primory pinion 33 Operation symptoms are overheating and piston seizure. You can make a quick check by disconnecting the delivery hose on the Autolube type and running the engine at various throttle openings. The Suzuki pump is behind a cover at the right rear of the crankcase and it has transparent tubing, so oil flow can be observed with — Clutch the engine running. Oil pump oil In case of failure (except Suzuki) you can mix with the fuel in the conventional two-stroke fashion and operate the cycle long enough to get it repaired. Kick starter pinion OIL PUMP OPERATION Suzuki The Suzuki pump Suzuki pump is driven off kick starter gearing. "91 is a rotating plunger type where the rotation of the drive worm and the plunger body is turned into reciprocating motion by a machined ramp on the end of the plunger engaging a plunger guide. The length of the plunger stroke is controlled by a cam which changes position according to throttle opening. The cam holds the plunger away from the guide and limits the engagement of the machined M M ramp when touch tion all of throttle of the the uum or allows it to when open. The rota- and uncovers inlet as follows: Oil discharging finishes and the plunger bemoving downward while rotating. Plunger operation enters the @ closed fully plunger covers and discharge ports gins is ramp oil intake stage. The plunger moves down more and created in the plunger. is oil pump a vac- cylinder above the The plunger nears bottom dead center and one of the two plunger intake ports aligns with the cylinder intake port. Oil is sucked into the cylinder by induction created above the plunger. Oil intake is finished and the plunger begins to move upward while rotating. CJJ in the cylinder begins to be compressed. The plunger moves up more and the oil is The oil pressure causes the differential plunger to be pushed up and move further compressed. Plunger rotation controls delivery timing in Suzuki pump. 34 The Two-Stroke Engine away from plunger and @ In this procedure, the the plunger. in the cylinder When is oil is compressed by the oil differential discharged smoothly. the plunger nears the top dead center position the plunger discharge port aligns with one discharge port. cylinder The compressed oil is discharged. When the pump driving worm is driven by the kick starter pinion, the plunger, engaged at a 90° angle with the worm, rotates. circular ramp A machined is into the bottom of the plunger. This ramp section engages the plunger guide screw and the plunger moves up and down by utilizing the plunger rotating action. The combination of rotating action and up and down movement opens and closes the intake port and discharge ports, changes displacement in the oil pump cylinder and changes the pressure of the oil. The oil is supplied separately to right and left crankshaft bearings through two oil discharge ports. The oil pump control cable, which is synchronized with the throttle cable, is fitted to the oil pump control lever. The control lever pulled in accordance with the throttle opening and turns a cam fitted to the lever. When the throttle is opened only slightly, the cam limits the is leng f h of the oil pump the throttle opening is plunger stroke. increased, the cam When turns and allows a longer plunger stroke, so that the amount of oil discharged increases. Check valves are located in the bolts which hold the oil lines and the crankcase bearings to the case. They should be (See illustration.) clean and filled with oil when removed and Fill the holes in the crankcase with about 10 cc of oil to make sure. Note: Be sure the gaskets on the banjo bolts are installed correctly. The grooved side of the gasket should be against the fitting. (See illus- replaced. Adjustment of oil pump control cable on Suzuki (typical). tration.) Correct tightening torques: check valve- -35 inch-pounds; banjo bolts 21 inch-pounds. — Yamaha Yamaha's pump is driven through reduction gears by the primary gear on the engine's crank- Rotary motion of the plunger is turned motion by an eccentric and guide pin and the distributor plate on the end of the shaft alternately covers and uncovers inlet and outlet holes. Length of the plunger stroke is controlled according to throttle opening by a cam which moves the adjusting pulley in or out to Clearance belimit or increase plunger stroke. tween "Adjust Plate" and the boss of the "Adjust Pulley" in the illustration determines pump stroke. The pulley is rotated by a wire to the throttle. A check valve prevents oil from seeping out of shaft. into reciprocal the pump case when it is not operating. Oil pump problems Oil (both types) Improper adjustment of control cable or broken cable © © Air lock of Pump pump Pump CHECK BALL DELIVERY HOLE 35 Operation PUMP WIRE WORM WHEEL I GUIDE PIN ADJUST PULLEY (or bubbles) ADJUST PLATE failure Suzuki Posi-Foree adjustment procedure Open the throttle fully and make sure there (Check both cables on is no play in the cable. © twins and synchronize throttles © if necessary.) Remove pump cover and observe the clear- }% DISTRIBUTOR ance between the control lever and the pin. This (.019"-.020"). It is better to be should be .5 on the tight side; if the gap is larger, less oil is mm GEAR SUCTION HOLE Cutaway delivered. © CAM ^WORM of Suzuki pump. L Adjust as necessary (at the point shown in the illustration) with throttle wide open. PUMP WIRE Yamaha Autolube adjustment procedure Two adjustment procedures are used for Yamaha pumps. type With all two cylinder en- gines the adjustment of the operating cable closed at throttle position; On justed at half-throttle. all later singles is made are ad- models there is a small circle marked on the throttle valve to show half-open position. On earlier models it the throttle travel and is necessary to measure ADJUST PLATE gage the halfway position. Measurement of the pump stroke is made (as shown in the illustration) between the boss on the adjust pulley and the adjust plate with a mini- mum clearance of .24 .12") as mm mm to .30 (.09" to mandatory. Synchronize throttles and adjust the throttle throttle closed. Match adjust pulley guide pin first Minimum clearance at is .24.30 mm {.09.12") for WIRE ADJUSTING SCREW cable at the grip for the necessary free-play. Leave © RETURN SPRING Q Yamaha pump. Twin cylinder engines on pulley by ADJUST PULLEY and V mark loosening the lock nut, then screwing the adjusting nut on the pump ADJUST SCREW LOCKNUT V-MARK control cable. Single cylinder engines © © Block the carburetor Match the V mark on guide pin by adjusting the the sleeve nut on the cable. If this .30 mm control cable at mm in less than .24 clearance between the pulis necessary to change the and the plate, it shim behind the plate. This is extremely rare and represents an assembly error, rather than ley wear. An ADJUST PULLEY GUIDE PIN the pulley with the pump adjustment results more than or PLUNGER STROKE throttle half open. lock in the pump ordinarily occurs only in the case of a replacement pump being not properly primed. Bubbles and poor delivery occur when air enters the line from a leaky joint. air Squirting oil on suspected joints or smearing them with grease will show up leaks which occur in Adjustment of pump on Yamaha singles (typical). apparently tight unions. Complete pump failure is comparatively rare but in the Yamaha pump, the adjust pulley guide pin has been known to fall out, so if the pump obviously quits, this is a first place to look. Refer to the following condensed troubleshooting guide for further details on Yamaha pump problems. 36 The Two-Stroke Engine Remedy r^ a. b. Clean pin hole Replace spring Trouble Plunger @ A-£able Guide Throttle Cable Adjusting Screw 1.0mm ^Ts Yamaha (Distributor or Cause Lock Nut Correct adjustment of throttle cable on not work. does starter plate rotates.) twins. a. b. Remedy b. Adjust nut or clogged guide groove for plunger guide pin Adjust-pulley guide pin missing cam a. .Pump Wire Worn Replace Replace pump pump case cover correctly Trouble Lock nut Distributor hard to rotate (?) Cause djust pulley guide pin worm wheel cam oil a. Incorrect adjustment of b. Incorrect fitting of plunger Remedy a. b. Proper clearance Replace or refit is 0.05 to 0.1 plate seal mm Trouble *-0.35mm Distributor partly hard to rotate Cause Worn or clogged guide groove cam guide pin Remedy a. Replace pump case cover a. Adjust Pulley Adjustment of pump Yamaha pump on stroke Yamaha twins (typical). cam Trouble Poor oil Bubbles in oil in the pump case a. Bleed the Check pump the following points for oil leaking: (1) Breather gasket (2) Suction pipe connector and (3) Distributor pump case (8) pump Pump and Pump case Pump b. tight fitting between adjust pulley and case cover a. Refit b. Replace Trouble Incorrect b. c. d. e. fails to work. (Engine works.) Cause a. Incorrect fitting of adjustment components Too a. case Trouble © in contact with pump setting Cause crankcase cover cover and pump case (9) Terminal of plunger; plunger cover, plunger cam oil seal and plunger oil seal (7) move a. oil seal (4) Distributor plug (5) Pump case (6) Banjo and fails to b. pump Remedy Remedy b. Adjust-pulley surface Cause delivery Cause a. Trouble © troubleshooting for plunger Defective worm wheel pin Clogged pin hole Worn pin hole Deformed return spring Defective cam of adjust pulley Defective plunger cam Wrong fitting of control cable to pulley Too big clearance between adjust and pump case cover Too much play in cable Remedy b. Replace Replace c. Refit d. Replace Readjust a. e. adjust pulley Chapter 3 Electrical Systems There are several electrical systems found on motorcycles today. One or two may be familiar to the average rider because of automobile experience, others have ramifications which are less well known. The first and oldest is the magneto for ignition and dry cells for lights. This is pretty rare but some models from a bygone era still use it. Most bikes with magneto ignition have a DC generator or an alternator for lighting. This is typical of many BSA, Triumph and other British bikes with Lucas electricals. The second oldest system, used by a great number motorcycles, of is exactly like that of the automobile with generator-battery-coil systems Yamaha, Suzuki and Kawasaki 125-250cc models are probably the most familiar examples. The alternator has been adopted by motorcycle manufacturers because of its reliability and using direct current. versatility. In the AC carbon contact cause internal short. on magneto Disintegrated kill-button Fixed-advance magneto uses tapered shaft and can system, there are several on a basic idea. One is to use the alternator as a magneto for ignition and put a rec- variations tifier output to in the circuit to convert its for lighting. A second for both ignition A and is DC to utilize the alternator lighting, employing AC for use the alternator to supply ignition and headlights but have a battery to feed neutral indicator light, horn and stop light regardless of whether the motor is running. everything. A third variation of this is is to to use DC for ignition in addition to stop light, indicator and horn. Generally speaking, the smallest displacement in the two-stroke bikes have the simplest system: alternator or AC magneto supplying output directly to the ignition, with other coils of the alternator devoted to (a) headlights and tail lights and (b) charging the battery. Several BSA models also use this system. models nut which requires special puller. Magneto The "conventional" magneto is gear driven and puts out a whopping good spark, increasing intensity with RPM, and is relatively free from malfunctions, which has caused it to be used on high-performance machines rather widely. Two types are in use: fixed advance and automatic advance. The former will be found mostly on racing bikes, and both types are largely Lucasbuilt as far as cycles in this country are concerned. A "Magdyno" made by Lucas, which incorporates a generator in an attaching case is found on many older British singles. The operation of the magneto is the same as if it Checking was ignition timing of magneto light/buzzer. 37 with static timing 38 Electrical Systems alone and the generator likewise. The most common problem encountered with magneto is poor performance caused by dirty, oily high-tension pick up and slip ring. Crank- Connection Diogram of Starting the case vapors seep into the case and deposit which collects other grime. Remove Replace the & Charging Systems s -OO 0-6 Starting Switch oil, oil seal. the pick ups and wipe clean. Make sure that the brush projects out of the case at Va" and works freely. Clean the slip ring by holding a clean cloth against it and turning - least ..-Battery the engine over. The breaker on mags are possibly not must be making good contact, properly gapped points as critical as other ignition systems, but kept fresh, Wiring diagram for starter-generator. and carefully aligned at all times. Broken wires or internal shorts are rare on magnetos, but the leads from the pick ups can fray or short out. The symptoms are complete lack of delivery. Before going into the end of the case, check to be sure that the kill-button wire not grounding. An infrequent occurrence, but one which has been known to follow an unskilled overhaul, is the destruction of the carbon contact for the kill button. Improperly installed, it can be disintegrated and short out the magneto. is Even making a quick check on a non-deis a good idea to put the it bike on the stand and rotate the rear wheel with gearbox in top gear. With the breaker point cover plate off, you can determine right away if the armature gear is slipping on the shaft, for livering in magneto, example. The fixed-advance magnetos utilize a tapered shaft and the gear must be tapped on and pulled off with a puller. If once secured, they seldom work off, but it can happen. The automatic advance type has a self pulling nut to draw the gear onto the taper and it also withdraws. So, loose Ordinarily, gear on shaft can be a problem. this doesn't just happen and cause non-delivery of spark, but results in out-of-time firing first. To test the armature coil and condenser, remove it from the housing and connect a wire from one terminal of a two-volt dry cell to the center screw of the breaker plate. Connect one side of an ammeter to the other battery terminal and the other side to the armature. Continuity should be proven and a reading of 4 amps indi- British bikes since ground; prior model negative ground. years and Polarity of 1951 has been positive Japanese cycles have all normal resistance. Using the same battery as a power source in the same way, make and break the contact at the center screw several times with an assistant holding one end of a short length of plug wire grounded against the armature body and the other about V%" away from the slip ring contact. If the high tension side is good it will build up the voltage enough to make a good spark at cates the gap. Worn cam in timing rings can cause such a divergence on twins that the magneto is blamed. .0 Velocette generator is driven by belt. (1) and turn generator in its clamp bolt of belt should be approximately Vi". © To adjust, loosen mount. Deflection Electrical Causes Trouble Item Plate Material Positive Plates Action Results Excessive charging Capacity decreases No way and discharging considerably Sediment causes Replace battery Find trouble and short correct at early Excessive charging current Solution specific gravity too high Drops to Bottom of Case at circuit bottom of to repair stage. cell. Over-discharging Capacity decreases No way Charging and Short circuit Replace battery. to repair. discharging with large current. Battery used at Warpage high temperatures Battery left discharged Sulphation in If slight Battery used without enough charge. drops and capacity in can small current long time If sulphation is great, replace battery. solution. Voltage at over-charging High High high. temperatures. Separators become solution brittle. specific Warped Replace battery. finish of discharging Carbonizing is for Repeated high rate •Battery can be of discharging. charged but capacity Repeated decreases rapidly Shrinkage battery very decreases. Voltage rises and bubbles seen when charging but will not take charge. too thick. Foreign particles sulphation be charged with gravity Specific Solution Plates White dots seen on plates. condition. Exposed plates. Negative Separator 39 Systems Replace battery. gravity plates. Battery problems, causes and remedies. Check timing closely and VrnT variation in piston if there movement is more than to affect point opening, replace the ring. Excess bearing wear and consequent armature vibration can be mistaken for other engine mechanical noises. The condition should be attend- ed to inasmuch as damage to the shaft results. If there is more than .005" vertical play at the end of the shaft, replace the bearings. DC generator system lighting only. generator-based electrical system is analogous to that of the automobile in some machines, slightly different in others. Japanese bikes of the medium displacement variety, such Yamaha, Suzuki and Kawasaki 125-250cc models, have a complete DC system with a starter-dynamo, voltage regulator, coil, condenser, British cycles generally DC Let's dispose of the systems which use a generator (or dynamo if you speak British) only for lighting or perhaps a starter-dynamo for starting and lights. Troubles here no horn, no generally start no around revolve caused by a flat battery or bad connections. DC Newer also. This pretty well divides up the troubleshooting into two categories: (a) full system, and (b) lights, The as ground have dynamos In any case, suspect the battery is responsible The 90% first since it of the time. place to check is at the battery termithey are slightly loose, corrosion occurs between the terminal and the cables and so much nals. first If resistance flow. It is put into the circuit that current can't takes a clean, firm contact, so make sure when connections fit this description. You can make a quick test of the battery by Japanese systems are negative ground, British models built since 1951 have been positive ground. Prior to that they were also negative ground. Harley-Davidsons have negative shorting directly across the terminals, for an instant, with a wire or the handles of a pair of pliers or the blade of a screwdriver. If you get a barely perceptible spark or none, the battery is, etc. or starter-dynamos DC is used. and magneto ignition all 40 Electrical Systems Specific Temperature Chart OX 10°C 20X (14'F) (50°F) (68°F) (86°F) 1.321 1.314 1.304 1.294 1.284 1.274 1.264 1.254 1.307 1.297 1.287 1.277 1.267 1.293 1 1.283 1.276 1.273 1 1.263 1.256 1.247 1.300 1.290 1.280 1.270 1.260 1.250 1.240 1.244 1.234 1.237 1.230 1.227 1.213 1.216 1.206 1.217 1.207 1.220 1.210 1.200 1.203 1.193 1.196 1.186 1.197 1.187 1.190 1.180 1.183 1.173 1.301 1.291 1.281 1.271 gravity Conversion (32°F) : 1.311 Specific Gravity 1.261 1.251 1.241 1.257 1.224 1.214 1.204 1.194 1.231 1.221 1.211 1.201 40°C • (104°F) 1.253 1 1 1 1 243 233 223 1 286 266 246 236 1.226 1 176 1.166 Specific gravity-temperature chart. Voltage regulator indeed, discharged. Obviously you can re-charge chargeable, but you will want to it, if it re- is know why it is flat. Battery The small storage batteries in motorcycles are of low ampere hour capacity and like all bat- they are self-discharging in storage. Most manufacturers advise that stored batteries be teries, charged once a month. Since many bikes are not used for several months at a time during the winter, this factor accounts for lots of complaints. Others are caused by carelessness in leaving lights on where this can be done with the key removed, direct shorts in wiring or faulty have a motorcycle battery re-charged on a quick charger at your neighborhood service station. The charging rate is too high and the battery will be ruined. Trickle-charge only, and then at a low rate such as 1.5 to 2 ampere/hours. You can go as high as 4 a/h for short periods. The battery will get pretty warm, but as long as it stays below 110° it will not be damaged. not, repeat not, Fill the battery to the specified level with water before re-charging. After charging, check the specific gravity of the electrolyte. A 12-volt battery should register above 1.250 at ambient temperature of 68°. A 6-volt unit should be above 1.230. Specific gravity will be lower at higher temperature, higher at lower temperature, so allowance can be made if temperature is drastically different from 68°. (See accompanying chart.) battery is consistently low and weak, may be in the voltage regulator. This is a simple electro-mechanical device between the generator and the battery designed to hold generator output to a specified voltage. The regulator is an electro-magnet with a set of contact points spring-loaded against its pull. When generator output reaches about 15 volts (in the 12-volt system) or 7.5 to 8 volts (in the 6-volt system) the pull of the magnet is sufficiently strong to separate the points and interrupt the There circuit. is an adjusting screw which regulates the gap between the points and, thus, the cut-out voltage. In action, the points are in a constant state of vibration and a regular flow of current is permitted. voltage regulator. Do the If the trouble To check the regulator disconnect the battery Then connect the negative lead of a voltterminal of the generator and the positive lead to ground. Start the engine and run it up to the point where the voltmeter stops flickering widely and settles down to a steady lead. meter to the D reading. This is the cut-out voltage and should be approximately the values given above. If the voltage is low, shut off the engine and turn the right-hand adjusting screw slightly to bring the points closer together. If voltage is gap wider. It doesn't take much of a turn on the screw to affect the gap, so take it easy. Start the engine, re-check and adjust as high, adjust the necessary. The output voltages given above are for ambient temperature of 60° to 80°. If it is hotter than 80°, lower the reading a bit, say by .5 volts. Or, conversely, it if a like amount. below 60° substantially, raise 41 Electrical Systems In addition to improper adjustment, the regufrom other ills: lator sutlers Regulator problems Here are some regulator troubles which can cause it to work improperly or not at all. 1. 2. 3. 4. 5. Core Gap Dirty contact points Burned contact points Broken or shorted wiring in Loose or bad connections Poor ground 0.6-0.7 coil Voltage Vibration of the cycle causes most problems and if the regulator is not operating at all, search for bad connections first. Dirty points can best be shined up by inserting a piece of paper or a business card between them and burnishing by rotating the paper or card. Burned points can be dressed with very fine emery cloth, used in the same way. A check can be made for a bad coil by running the engine and holding the armature down so that points open. If they won't stay down the series winding is bad. If the coil pulls the contacts apart but voltage doesn't drop (as indicated by the voltmeter), the shunt windings are broken. Cutout The other part of the regulator is a cutout, a relay, which permits the flow of electricity in Down 4- Yoke- Point • Complete DC The dynamo. exception. The magnetic force exerted used to overcome the resistance of a spring and close a circuit so that current can flow from the generator to the battery. Otherwise the circuit is broken, preventing current drain new element from the circuitry. is battery. This cutout is relatively trouble free, except for occasional sticking points. It takes about 12.5 volts from generator the operate in the to 12-volt system make the cutout and about 6.5 in The are 8 system same Triumph Thunderbird early is an cutout and battery problems previously described, but the regulator, the as and condenser enters the of coil Also, there is more opportunity for the battery to discharge because of the added connections. Generator problems first place to check Disconnect the battery from the regulator B terminal (or A if bike has an ammeter) and connect the positive lead of a If the 6-volt system. Gap 0.7-0 This system uses generator-battery current to supply ignition needs as well as those of lighting. In nearly all cases, the generator is a starter- only one direction. coil 1.0 Cutout relay (typical). by its Gap 0.9 the battery is flat, the the voltage regulator. is voltmeter to the terminal. Ground the other lead, either at the regulator E terminal or a suitable Core Gap * spot on the bike. 0.6-0.7 Start the engine and run it up for a check regulator output as described before. no ligh-Speed contact Point Contact Point — lr-- Point Gap 0.4-0.5 Voltage regulator (typical). on is check the generator output by keeping the engine running at about 3,000 rpm and removing the wire from the generator F terminal and grounding it for an instant. If voltage rises to over 25 v (for 12 v) or 13 v (for 6 v) then the generator is good and the regulator is at fault. If voltage does not jump up, the generator is juice, bad. Some Harleys have Low Speed If there a voltage regulator, some Those which have no regulator employ a three-brush generator of the type found on Model A Fords. This is a reliable setup and two field coils are used, one for ignition, the do not. Electrical Systems 42 added when lights are turned on. The moveable (narrow) third brush controls output. other Moving the brush in the direction of rotation inmoving it in the opposite direction creases output, reduces it. Here are possible causes of generator trouble. 1. Poor connections or shorted terminals 2. Oil or water in case 3. Carbon dust from brushes 4. 5. 6. 7. 8. is shorting out windings Poor brush contact with armature Worn-out brushes Commutator of armature is dirty, pitted, or rough causing brushes to make poor contact. The gaps between the armature commutator segments are filled with carbon. Field or armature coils have broken wires. Typical starter-generator. For a quick test of the generator, try to motor This it by closing the points of the cutout relay. causes current to flow from the battery and it should spin. Disassembly and examination of the generator should make any of the above conditions obvious except broken wiring. To check the field coil for continuity, a set of test leads is necessary. Remove the wires from F and A terminals and If there attach the tester. is a broken wire in the is no continuity, there field. If this tests o.k., check the wiring of the yoke for poor insulation which can be shorting. The armature is tested for continuity ing the shaft and the commutator. continuity there is If by probthere is a short in the windings. Dress the armature commutator with fine emery and undercut the mica insulators with a pocket knife or a ground hacksaw blade so that the segments are clearly separated. The presence of solder on the inside of the housing indicates that the generator is throwing solder and is shorted internally in the armature. Replace the armature if in doubt. In replacing the generator, if it is necessary to replace a negative ground with a positive ground, or vice versa. Motoring the unit for a few seconds with the current from the battery cloth will polarize it to the new polarity. Starter-generator This combination is not merely an arrangethe generator is motorized. A generator has very little torque with the normal windings, so a starter-dynamo has two sets of field windings and brushes. The starter windings and brushes are much heavier than the generator components, but are subject to the same problems. Poor internal connections can also plague the ment where starter-generator and these units are more suscepCheck the same items in the tible to carbon starter portion as in the generator portion vis- ually dust. and for continuity with the test leads. (1) Brush, (2) brush spring, (3) field coil, pole core, (5) terminal, (6) internal gear, (7) ball bearing, (8) sprocket shaft, (9) sprocket, (10) gear housing, (11) planetary gear, (12) center bearing holder, (13) york, (14) armature, Starting motor. (4) (15) cover band, (16) commutator, (17) commutator end frame, (18) bearing bush. Separate starter A is found on many modern analogous to the generator in its troubles and should be handled the same way. Starter drive chain wear and sprocket wear can be a problem on high-mileage bikes because the ordinary overhaul does not include a chain unThis may less the condition is fairly critical. be the source of noise when starting, but most riders do not strip down to repair it until the separate starter cycles. It is chain or sprocket finally fails. Alternator The alternator flywheel magneto is the and modern outgrowth of is the the least troublesome, method of generating power in displacement machine. It is reliable in that there are no brushes or slip rings and no segmented commutator, also the rotor is a most the efficient small 43 Systems Electrical Alternator schematic diagram and parts identification, Ducati. Stator. screw, (6) (1) 1st charging spring washer, (7) Casing, (12) pole pieces, (13) coil, (2) terminal block, (3) low voltage three-pole cable, 2nd charging coil, (8) stator plate, magnet, (14) hub, (15) rivet. permanent magnet and has no internal wiring. Alternators are mounted on the crankshaft in some models, driven by the crank in others. The operation depends on the principle that if a magnetic field is interrupted a current is generated. In the alternator, the rotor spins inside a housing which has six coils mounted inside it. Current flows in one direction as the field is interrupted going in and in the opposite direction going away. This is changed into direct current for use with storage batteries by a selenium or silicon rectifier or a Zener Diode, devices which permit the flow of current in only one direction. In some models, such as Honda 50-55 and 65cc, BSA, Suzuki 50, etc., an "energy transfer" system is used where the AC is fed directly to coil, points and plug for ignition and to headlight and taillight. DC is used for charging the (9) coil fixing (4) insulating sheath, (5) screw, (10) tin-plated copper wire. fixing coil Rotor. (11) open at peak output of the current build-up, and so the current flows only are fixed, timed to one way through the coil. This division of current is accomplished by a multi-position ignition and lighting switch which and out of the Generally two of the coils are wired into cuts the coils of the alternator in circuit. the battery-charging circuit, and two for Many two to the ignition lights. AC systems are 6-volt, others are 12divided along displacement lines with the bigger models having the 12-volt system. BSA volt, AC and others with Lucas 12-volt Diode, rather than the To check to have an use a Zener rectifier. the alternator output AC it is necessary voltmeter and be able to operate with supplementary battery ignition. In general a 6-volt alternator should put out about the engine from battery which supplies juice for indicator lights, 4 horn and stoplight. position) plus 2.5 additional for the second In this setup the points are wired in parallel with the coil rather than in series and the points 2 volts volts 3,000 from RPM. the the "ignition" third. coils This (first is at switch and about 44 Electrical Systems Rectifier and diode troubles Heat is the enemy of these units. Keep the aluminum heat sink of the diode clean. Be sure the mounting bolt of the rectifier is tight. Don't take the battery out of the system and operate the bike for long periods with Hondas, particular- - '£ ConlOcJ fareoVer because of ly, - the danger of overheating the rectifier. Ignition Core primary coi N Exploded view of flywheel magneto (Suzuki). Connections for test leads can be made as follows: Disconnect the three alternator leads from the snap connectors and connect a 0-15 AC voltmeter with a 1 ohm load resistor in parallel with the three leads, each in turn. Low readings on any group of coils indicate that wiring insulation may be chafed or broken or that some of the turns of wire in the coils are short circuited. No reading any group of coils indicates that they are grounded or an open circuit exists. Low reading for all coils can indicate that the rotor has Secondary co 'Ignition partly demagnetized. Lucas RM 13 alternator The Lucas AC ignition system is connected to ensure a fully charged battery under all normal running conditions. In the case of machines fitted by the smaller Model RM13 alternator, the charge rate may not always be found quite sufficient to meet the requirements of low-speed town work, the running-in period, short winter runs involving long periods of parking with the lights on, and similar conditions. In this event, by interchanging two of the three alternator cables where these are joined by means of snap-connectors to the main harness. To do this, switch off the lighting and ignition switches and disconnect the dark green and medium green cables by pulling these cables from their snap-connectors. The dark green alternator cable must now be connected to the medium green harness cable, and the medium the charge rate can be increased green alternator cable to the dark green harness cable. due to a change in running conditions, the battery is found to be overcharged, as indicated by excessive gassing of the electrolyte and a frequent need for topping-up, the original connections must be restored. If, Primary (Flywheel Pole coil magnetol Schematic of energy transfer ignition system (Suzuki). Selenium or for become coil) silicon rectifier Rectifiers are generally fitted with two AC in- put connections and one DC outlet. On Lucas rectifiers the center terminal is the output side and other types are easily identified because of the disposition of the wiring. To check the rectifier for continuity, simply connect one lead of a voltmeter in place of the battery lead and go to ground with the other. Then start the engine and read the voltmeter. should pass 7 to 7.5 volts. To check it for leakage (permitting DC current to flow back from the battery), connect the mounting bolt to the appropriate terminal of a battery (positive or negative depending on the ground arrangement). Then, using a .05 amp test bulb, or similar bulb, complete a circuit from the other battery terminal to the AC terminals of the rectifier in turn. If the bulb lights, there is excessive back-flow and the rectifier is not valid. It Zener Diode Assuming the battery is in a low state of charge terminal voltage (the same voltage as across the diode) will also be low. Therefore, the maxicharging current will flow into the battery from the alternator: at first none of the curits mum is by-passed by the diode because of its being non-conducting due to the low battery terminal volts. However, as the battery is quickly rent restored to a full state of charge, the system volt- 45 Electrical Systems age rises until at 14 volts the Zener Diode bepartially conducting, thereby providing an alternative path for a small part of the charging current. Small increases in battery voltage result in large increases in Zener conductivity until, at approximately 15 volts, about 5 amperes of the alternator output is by-passing the battery. The battery will continue to receive only a portion of the alternator output as long as the sys- comes Terminals tem voltage is relatively high. Depression of the system voltage, due to the use of headlamp or other lighting equipment, causes the Zener Diode current to decrease and the balance to be diverted and consumed by the component in use. the electrical loading If is sufficient to cause the system voltage to fall to 14 volts, the Zener Diode will revert to non-conductivity resistance full of output state generated go to meet the demands of the battery. will Sectional view of rectifier. a high and the Testing the Zener Diode Reading should be below mA ] The test procedure given below can be used when it is required to check the performance of the Zener Diode type motorcycles) while Selenium rectifier ZD715 equipped originally volt it and (supplied for 1212-volt in position is converted on the ma- chine. Good quality moving coil meters should be when testing. The voltmeter should have a used scale 0-18, test 1. and the ammeter 0-5 amps/min. The procedure is as follows: Disconnect the cable from the Zener Diode and connect ammeter (in series) between the diode Lucar terminal and cable previously dis- The ammeter red or positive (+) must connect to the diode Lucar terminal. connected. lead 2. Checking rectifier milliammeter reverse for — reading current flow with (leakage) should be less than 10 ma. Connect voltmeter across Zener Diode and heat sink. The red or positive lead must connect to the heat sink which is earthed to the frame of the machine by its fixing bolts and a separate earth lead. White with red Red to the tracer 3. Selenium The black Start the engine, ensure that all lights are off, and gradually increase engine speed while the same time observing both meters: rectifier e a. >/ e Lights connected ammeter must indiamps, up to 13.0 volts, which will be indicated on the shunt connected voltmeter as engine speed is slowly in- The series creased. b. Increase engine speed still further, until Zener current indicated on ammeter is 1.0 amp. At this value the Zener voltage should be 13.5 volts to 15.3 c. is to connect in circuit light bulb. with battery and at cate zero Batter\ Simple rectifier test lead connects Zener Lucar terminal. volts. Disconnect the battery while the engine is running, and slowly increase engine speed until Zener current indicated on the amme- 46 Systems Electrical ter is 5.0 amps. At this value the voltmeter should indicate a Zener voltage of 12.0 to 15.0 volts. Note: Test "c" should be carried out as as possible to avoid overheating the Zener Diode. quickly If the ammeter in test "a" registers (D Conloc' breoker ® P'.mory coil any current at all before the voltmeter indicates 13.0 volts, then a replacement Zener Diode must be fitted. If test "a" is satisfactory, but in test "b" a higher voltage than that stated is registered on the voltmeter, before the ammeter indicates 1.0 amp, then a replacement Zener Diode must be fitted. "c" the Zener Diode does not pass within the stated voltage limits, it should If in test 5.0 amps be replaced. Checking the energy transfer system To check AC Flywheel system as used by BSA and others, it is necessary to take the alternator out of the system. If the engine is a twin two 6-volt batteries are needed and the hookup 1. 2. out the made is coil as follows in the in ® this mogneto Pnmofy Ignition coil coil ! I (D ® Ignition ptimoty co Seoondory coil Electrical current flow in energy transfer ignition. BSA: Disconnect the alternator leads. Disconnect the black/yellow wire from the condenser at the hand right to the positive terminal of coil and connect it one of the batteries. Connect the negative terminal of the battery to the condenser. 3. Disconnect the black /white wire from the other condenser and connect it to the positive terminal of the second battery and the negative terminal of the condenser. This assures a supply of current normally delivered by the Remove alternator. lead from one spark plug and open and close the breaker points a couple of times. If a spark can be induced between the lead and the plug or to ground, then the coil and condenser serving that plug are in good shape. If no spark, then substitute a known good coil OVERLAP the MUST BE EQUAL ON BOTH SIDES WHEN POINTS ARE BREAKING Critical timing of points with rotor is required in energy transfer system. or condenser. This same procedure can be any bike having this arrangement. Note: It as quickly is as very important to followed make this with Correct test possible since these coils are not designed to operate on DC and can be overheated and ruined. Miscellaneous alternator items These are particularly trouble-free units, but wiring and switches in some models cause problems since contact must be good. In addition, a slight movement in the switch can cause a change in alternator output by cutting in or out the various coils. Continuity and resistance tests can be run with shop equipment but the average rider must rely on visual inspection and the deductive reasoning. Contamination Breaker point contact conditions. 47 Electrical Systems Less frequently encountered troubles include a loose rotor caused by insufficient tightening of the shaft nut and too little clearance between stator poles and rotor. This clearance should be approximately .007". Make sure pole studs are tight and not permitting poles to rub on the rotor. HT. CABLE Breaker points Fig. 63 CONNECTOR Wear, the attrition of countless electrical discharges between the contacts, is the enemy of breaker points. Poor condensers hasten the end by not completely absorbing the current induced in the process. on one point is A an indication of poor condenser which are blue from Points are cheap and easy to replace. them DISTRIBUTOR COVER build-up of metal ("transfer") capacity, as are points try to save Distributor if heat. Don't they are far gone. you clean the points every 2,000 miles or so with fine emery cloth, or even just burnish them with a business card rotated between the closed contacts whenever you adjust the gap, they will survive much longer than if you ignore them. ROTOR ARM If If points burn consistently, check the connecand ground. Excess voltage CAPACITOR CONTACT BREAKER LEVER FIXED tions at the battery diverted to points as the least-resistance CONTACT*LATE SECURING SCREW path could be the trouble. On twins, where two sets of points are used and it is necessary to alter the gap of one to match the timing on the other, this is permissible. It is better to have a variation in gap than in BASE PLATE SECURING SCREWS timing. Likewise on magneto models, if gap is within it is better to let it alone than to re-time the .003", mag. from weakening of automatadvance springs and a general oil-soaked con- Distributors suffer ic dition on motorcycles. you can do unit up, all is a high-mileage unit. Outside of cleaning the is replace the springs With the if it conventional Conventional distributor as used on Norton. cap for tracking, if poor ignition problems can't be laid at any other doorstep. This is really pretty rare although cracked and broken caps aren't. But they are distributor, scrutinize the bakelite also pretty obvious. Spark plugs The spark plug is seldom worn out in service but generally fails because of imposed operating conditions. Carbon formation, lead fouling from gasoline additives and other destructive forces cause the electrodes to cease being the easiest path for current to follow. Best advice about plugs repair. The accompanying is replace rather than illustrations A disclose various plug conditions and causes. study of them and a comparison between the photos and your bike's plugs will do much to educate you on engine operating conditions. Hot Type (for low temperature Cold Type Medium Type (for high temperature use) Construction of plugs having different heat ranges. 48 Electrical Systems Always use the plug recommended by the manufacturer for normal conditions. If the rec- ommended plug is clearly too hot or too cold for the conditions your cycle encounters, go to the next step in the heat range. Set the gap right, rest keep it clean and of the ignition system you'll is have fire working. if the Coil Coils suffer from overheating, principally. Leaving the ignition on is an invitation to a melted coil since the current from the battery will flow through the points and into the coil. To check the condition of a dubious coil, substitute a known good one. Mixture too rich, plug too cold for conditions. Mitxure too lean, plug too hot for conditions. Plug of proper heat range, mixture good. Oil-fouled plug. Chapter 4 Clutch and Transmission Clutches and transmissions on the modern motorcycle can be said to be highly developed and relatively trouble free in contrast to the general situation a generation of riders ago. — Clutch Spring Plate 5 I? Pushe Boi' Cutaway view of Honda centrifugal The modern unit-box is clutch. of the constant-mesh and greatly simplified. Clutches are almost all of the same pattern, wet multi-plate on the countershaft, with some centrifugally operated types on the smallest displacement models, and a lesser number of dry multi or single variety plate types. To the clutch or transmission means on most Japanese machines and a fair amount of labor on the others. So it is best to be aware of the early symptoms of impending trouble and take corrective action, if possible, get at a strip-down before the worst occurs. The best preventive medicine for clutches is to keep adjustment cor(with enough free play at the lever to allow complete disengagement), and to make gear changes with a blip of throttle instead of speed shifting. This is elementary advice, but if not followed, some of the following symptoms will be sure to show up. rect Engine speed increases when opened but machine doesn't (T) Clutch Bushing a- Caused by Clutch Thrust W.isher (a) worn (c) oil if wet type too much oil if dry type not fully releasing (e) 49 insufficient spring pressure (b) (d) Exploded drawing of Kawasaki clutch. throttle friction discs lack of is 50 Clutch and Transmission mmi 12 16 10 14 15 13 II 18 2 17 3 I 4 4 3 6 5 19 Early model Triumph clutch. Imm^ Sp&ii^ 12 12 13 12 13 13 14 15 16 17 Later model Triumph clutch. clutch housing Let's drj clutch plate ring clutch boss / he reduction rpinion yj~| Crank first, lack of suf- There should generally be Vi" or so movement at the outer end of the handlebar lever (or Vb" clearance at the inner end) friction disc h rus . j i (outside), take the least-serious ficient free play. shaft before the clutch actuating mechanism begins to to the clutch. This can be adjusted do anything where the cable enters the housing actuating mechanism inside the at the lever: and/or housing. is at the It is important to make sure that there no pressure on the release mechanism point of disengagement. Too much at the free play will engagement, or more preabrupt and grinding noises. If your setting of the free play adjustment changes one condition for another, you've gone too far and something result in difficult gear cisely, in between is indicated. In British bikes and others with rod-actuated clutch mechanism (see the Royal Enfield illustration), the screw which is at the end of the Clutch arrangement of Yamaha 250 models. pushrod passing through the mainshaft must be unscrewed slightly if there is no actual free play. The clutch release cable must be slackened off 51 Clutch and Transmission Primary drive gear Clutch outer complete Primary driven gear Clutch outer Clutch friction disc(7discs) Clutch plate! 7p(ates Clutch plate A' 1 plate Clutch plate Bi6plates) Clutch center Clutch springs 6springsi 1 Clutch pressure plate Clutch lifter joint piece 6mm Clutch #10 (fj) ' (fj lifter liftet 5 16 thread complete Clutch adjuster Clutch adjuster fixing piece Exploded view of Honda 450 clutch, typical above 90cc. of models all is made in order not to inClearance of Mra" to lis" at the sleeve at the housing should be set and any slack in the cable taken up at the handlebar adjustment. Insufficient spring pressure or worn friction discs are indicated if the adjustment is correct and the clutch still slips, particularly when speed shifting. Another time at which lack of binding Clutch Lever while this adjustment fluence it. pressure becomes noticeable, clutch which is if you aren't in the kick starting. The on the countershaft, as in most geared up to the mainshaft and habit of speed-shifting, is in small bikes, is torque is multiplied. Clearance of '/| case Internal Adjusting clutch lever free play at housing on Kawasaki. 4 " to for of poor friction discs there is little which can be done in the non-adjustable pressure In washer rod steel bal Clutch flat is specified adjustment on Kawasaki. A quarter-turn screw outward is nominal adjustment. clutch of i/ " at inner end of lever 8 Kawasaki clutch release. 52 Clutch and Transmission Exploded view of Royal Enfield clutch, typical of pushrod- operated clutches. ADJUSTER NUT /INCREASE BSA other British bikes) requires approximately clearance at inner end of clutch release lever. (and Vs' plate type except to replace the offending parts. In British cycles and others with adjustable re- off you can tighten up on the screws and an overhaul for some time if you let the slipping condition get out of hand. lease arms, stall don't The wet type clutch depends on oil for proper functioning. The dry-plate type can't stand it. The BMW, Ariel and such, with dry clutches tolerate a small amount of seepage from seals, but if they become oil-soaked, you've had it. A little oil can be burned off by slippage, which generates heat, they say, but getting exactly the right amount of heat this way to cure an oily is more apt to be luck than science. you are hard put to locate a clutch disc for your not-so-common dry-disc job, you can soak clutch If the friction material in or carbon tetrachloride a strong solution of solvent CCU, (not gasoline), or even boil detergent to it in remove the oil. With the wet-plate the chain case right type, keep the oil level in on the mark. Use the rec- F 53 Clutch and Transmission © ® Clutch adjusting mechanism (internal) of Honda. ommended weight oil, and, if in doubt as to what should be, it is no crime to experiment. The lightest oil you can use without problems is the it best. when (D Gear grinding shifting This symptom generally stems from clutch sources rather than transmission problems. The prime Single-plate dry-disc with clutch diaphragm spring used possibility is failure to release fully. Too in BMW. F BSA clutch pressure plate is retained by these retaining nuts (P). M G four spring Locations ST LEVEL SCREW adjustment points in BSA the screw pin and G the locknut. clutch of is DRAIN SCREW twins— 54 Clutch and Transmission Exploded view of Royal Enfield transmission much free play in the clutch cable is the most probable cause. Cut down on the free play of the lever. Again, be sure the adjustment mechanism at the case is correct. The point where pressure released should be between Vz and adjusting screw on pushrod-release 1 is just turn of the clutches. Gear change cam and ratchet Operation of shift mechanism on Honda automatic clutch 10 of shift lever movement disengages clutch, balance of movement changes gear. in BMW transmission. models— first Disposition of change mechanism in BMW box. ' 1 55 Transmissions CM CM -«rr r— < --^ -n CM a th Tt cause trouble. Riders who adjust the screws in the pressure plate arms to take up wear can overdo it and coil-bind the springs, clutch spring pressure, causing partial has been previously overhauled, there are other items to think about. In many clutches, such as Royal Enfield, clutch springs are clutch alternately, (fixe must be behind the screws. Any miscue here can weak and strong, and in the models with adjusting screws, the strong springs which causes drag and poor releasing. TRANSMISSIONS The most common complaint about transmisis difficulty in engaging a gear. As opposed sort of malfunction. fitted > G< the few miles two factors. a a. CO a> non-disengagement, is present whether cold or hot and regardless of adjustment. Some clutch springs can be individually adjusted and are prone to this If o •* cause If when the bike has been run and warms up, suspect either of Uneven CQ — Yamaha 250 4-speed transmission. condition clears up these — O a • en pear Second driven gear Change _ driven Rear Shifter cam plate Shifter cam stoppi Move-over spacer for Honda transmission out of gear. stops jumping Simple and effective gear change Yamaha 3-speed method box. is employed in 57 Transmissions PRIMARY PINION DRIVE SPROCKET Powerflow finding a gear, it in means a strip-down Yamaha 4 speed transmission of 125cc model. to get at the linkage and/or spacers, broken ratchet spring, etc. A close perusal of the accompanying of various gearboxes will make illustrations the operations clear and demonstrate the need for internal repairs. Shifter cam st opper pin Change lever (A) RETURN SPRING PAWL HOLDER SHIFT PAWL f RETURN 'CHANGE SPRING LEXER SHIFT PAWL SHIFTER RATCHET WHEEL Shifter cam plate Rotary motion is converted into linear motion by shifter plate. Wear in plate, stopper pin and change lever can account for jumping out of gear and difficult engagement. cam Indexed cam moves shift fork to change gears 4-speed. in Yamaha Clutch and Transmission 58 the cogs into mesh when the clutch is maladjusted accounts for a lot of it. In Hondas, too, the shift drum limit spring can lose tension Jamming and create trouble. @ Transmission won't You shift strip-down anyway, but it might be good to know what to look for. If the clutch operates but the shift lever won't are move any in engagement is by dogs tapered in Suzuki 3-speed. Transmission jumps out of gear This means different things with different boxes. In the Japanese constant-mesh transmissions where (T) gears are engaged by coupling with dowels, either the gear is not being shoved far enough into mesh or the dowels are worn off. In boxes which use plungers and balls for locating, the springs can be too weak, a pawl of the shift arm or the broken. Or, in the small displacement bike, the dowels on the end of the drum which engage the shift lever may be sheared off. This is rare, but it can happen. In addition, in various bikes, the numerous pins which provide the fulcrum points for linkage can break. If you can get the box into one gear or more, depending on the type, then the problem lies in gear, the shifting fork Gear for is the engagement of the other gears: pins, clutchdogs, etc. shaft second gear cause it takes more is broken dowel In the Honda, the counterusually the first or engagement Worn cam plates Worn spacers, in BSA is not being forced. boxes show up this way. particularly in Honda suspect be- of a beating. Gear shifting pav boxes, are responsible for the most complaints. particular problem with spacers and a thicker one is There is a Honda second gear available from Honda to correct the condition. Worn Gear shifting cam pm (A or bent shift forks are also a prime cause, which may have been ridden by inexperienced youngsters. particularly in small displacement bikes Gear shifting cam stopper When Gear shifting pawl When mechanism of small displacement Suzukis. up ear Gear Kick-starter shifting shifting shifting cam stopper shifting down Broken shift lever spring or worn pawl and pins can cause problems in Suzuki box. Transmissions 59 Transmission counter shaft Row gear M2 2nd gear M3 3rd gear M« Top g^ar flMil ] . Disassembled gears In the Royal Enfield and such boxes where the ratchet plays such an important part, a weak or broken ratchet spring can permit the shifter to slide right past a couple of gears and lead you to in Honda 450 box. Drain the gearbox and examine the oil for bits Poke your little finger into the sump and run it around the inside of the case adjacent of metal. to the hole for the drain plug. suspect the worst. metal, be prepared. Seldom are gear teeth chewed up, but when breakage does occur, the resultant growling and howling or malfunction is pretty obvious. (3) Jamming The If there are bits of kick starter tooth on the kick starter sector bears the brunt of service because it is the engagement first point and if tinue to be once fouled, it is more likely to conchewed up. The tooth can be ground off if this is the only problem, rather than replacing the whole sector. If the pinion teeth are bad, the starter seldom jams, slippage is the symp- tom. Weak portion of Triumph box is layshaft pinion gear. Gear changing mechanism of Suzuki 3-speed. 60 Clutch and Transmission ,***** r, a s e Kick-stopper 1 """ w t-vevss VL\cV» \, / er /KicU-»-o^ ',etain er 7 / Kick-roller retainer- *"" Kick-starter @ mechanism, Yamaha Moped MF-2. Slipping kick starter ratchet pawl (in British cycles) engine does not spin over in response to a kick, and there are grinding noises, worn out or broken sector or pinion gears can be suspected. If the If the starter doesn't want to engage, a bearing worn If the return is to be suspected. spring breaks and the pedal doesn't flip up, it should be replaced at once. Secure it in place while operating the machine. Accidental engagement can mean big trouble. Chapter 5 Carburetors and Tuning The carburetor is, if GENERAL CARBURETOR TROUBLESHOOTING not the heart, at least the lungs of the motorcycle. It is tinkered with too much and not kept clean enough by most riders. There are only a few mechanics who understand carburetion enough to alter the factory settings and improve performance, yet nearly everybody takes the liberty to manipulate. There are two possible faults in carburetion, weakness of mixture. either richness or Indications of richness Consequently, © Black smoke exhaust © Fuel spraying out of carburetor stroking © Four-strokes, © Two-strokes, four stroking © Heavy, lumpy running © Sooty spark plug most carburetor trouble can be traced to the last "tune up" or the last time somebody fiddled with in the carburetor. eight A good understanding of each carburetor's mechanical method of coping with an engine's varied demands for fuel/air mixtures will help put you on the right track for troubleshooting. We Indications of weakness review each of the popular carburetors in the terms used by the manufacturers. Follow the thinking of the designer and you will better understand where and how trouble can crop up. Amal carburetors have always been in the forefront of motorcycle fuel systems. Now, probably will the Keihin the Amal is is back carburetor © © Erratic slow-running © Overheating © Engine runs Spitting better open or choke used on more individual cycles but in every corner of the world. slide-throttle type owe Amal. They use different methods to attain the same ends in many cases, but the simplicity of operation and ease of service are all due to this concept. throttle slide causes problems in tuning if throttle is not wide partially closed. is jets present check if and passages are gauze in float chamber banjo connot choked with foreign matter, and clear, that filter allegiance to Worn is If richness or weakness caused by: a. Fuel feed. Check that found Other carburetors of the in nection is there ample flow of is fuel. Be sure there is no flooding. Carburetor is usually kept clean enough by Mike Capalite advocate Amal carburetors. 61 with too much and not average rider. Experts such as maintaining factory specifications. tinkered Carburetors and Tuning 62 Air leaks. b. to the engine or These may be due to excess at the inlet connection valve stem- Defective or worn parts. loose fitting throttle valve, Examples are a worn needle jet, loose jets. d. Air cleaner choked up. e. An from the tank lodging on the float needle its valve from closing. It may also be caused by a worn float needle valve. High consumption will be apparent if the purities seat preventing needle is a minimum when any movement of backlash the controls are set back and that of the handlebar does not cause the throttle to open; this is done by the adjusters on the top of See that the throttle shuts cannot be corrected by normal adjustbe due to flooding caused by im- may jet has worn. It may be remedied or improved by lowering the needle in the throttle, but if it cannot be, the only remedy is to get a new Cable controls See that there it needle having been removed. air cleaner the carburetor. If this ment, guide clearance. c. Excessive fuel consumption jet. There are many other causes of high fuel consumption not connected with the carburetor. down freely. Fuel feed Some model Amals and others are fitted at the inlet to the float chamber. To remove the filter gauze unscrew the banjo bolt; the banjo can then be removed and the filter gauze withdrawn from the needle seating. Be sure that the filter gauze is undamaged and free from all foreign matter. To check fuel flow, before replacing the banjo, turn on fuel tap momentarily and see that fuel gushes out. with a later filter gauze Flooding This may be due to a worn needle or a leaky but is more likely due to impurities (grit, fluff, etc.) in the tank; so clean out the float float, chamber periodically the trouble ceases. till If the trouble persists, the tank must be drained and cleaned out. Fixing carburetor and air leaks Erratic slow-running is often caused by air so verify there are none at the point of leaks, inlet pipe. Check by and eliminate by new washers attachment to the cylinder or means of an oilcan and the equal tightening of flange nuts. On later model Amals a sealing ring is fitted into the attachment flange of the carburetor. In old machines look out for air leaks caused by a worn throttle or worn inlet valve guides. Backfiring in exhaust May be caused by too weak a pilot mixture is closed or nearly closed. Also it may be caused by too rich a pilot mixture and an air leak in the exhaust system. The reason in either case is that the mixture has not fired in the cylinder and has fired in the hot exhaust header or muffler. If the banging happens when the throttle is fairly wide open the trouble will be when the throttle ignition, not carburetion. Three controls low variable idle speed range. parts speed; mixture; (B) (0 of Amah pilot main throttle stop screw (A) screw controls idle and controls upper speed jet air . 63 Arnal Carburetors Air is filters These may set with an affect the jet setting. air filter If a and the engine carburetor run with- is out one, take care not to overheat the engine due to too weak a mixture. Testing with the choke will indicate if a larger main jet and higher needle position are required. Clip and Notch Adjustment for Needle Position J ji.' ^^^ *&»*£. ^s^ Jet Carburetors are set by the up to 3,000 feet (apCarburetors used constantly for proximately). altitudes of 3,000 to 6,000 feet should have a re- Throttle Needle P^ -*"—""" Block < Pilot Air Passage required. factory suitable for altitudes duction in main jet size of 5%, and thereafter for every 3,000 feet in excess of 6,000 feet altitude further reductions of 4% should be made. No adjustment can compensate for lost power due to V' ~ hrottle Slide Increased altitude tends to produce a rich mixture. The greater the altitude, the smaller the jet — on carburetor Effect of altitude main ^^^^ ~~—~— Throttle Return Spring rarified air. fsff Fibre Seal Tickler Assembly Carburetter Body Screw Pilot Air AMAL CARBURETORS Jet Block Locking Sere. Monobloc-RN-TT-GP The supply of air to the engine is y^i controlled by a throttle slide which carries a taper needle operating in the needle the throttle slide The needle jet. by is Float secured to a spring clip fitting in Chamber one of grooves and the mixing strength throughout a large proportion of the throttle range is controlled by the position of this needle in the slide and by the size of the jet in which it works. There is, however, a restricting or main jet at the bottom of the needle jet and the size of this controls the mixture strength at the largest throttle openings. At very small throttle openings fuel and air are fed to the engine through a separate pilot system, which has an outlet at the engine side of the throttle. The air supply to this pilot system is controlled by the pilot air screw, and the slow running of the engine can be adjusted by means of this screw and a stop which holds the throttle open a very small amount. five The throttle slide is cut away at the back and the shape of this cutaway controls the mixture at openings slightly wider than that required is a compensating system to prevent undue enriching of the mixture with increasing engine speed, this system consisting of a primary choke surrounding the upper end of the needle jet through which air is drawn in increasing quantities as the depression in the main choke increases. This air supply and the supply to the pilot system are taken from two separate ducts in the main air intake to the carburetor so that all the air passing to the engine can be filtered by fitting an air cleaner to the main carburetor air throttle for slow running. There intake. Amal Monobloc. Two small holes in the needle jet, at a level just chamber, permit fuel to flow into the primary choke when the engine is not running or when it is running at very low speeds, thus forming a well of fuel which will be drawn into the engine on starting or accelerating from low speeds. At moderately high below the static level in the float engine speeds the level of fuel in the float chamber falls slightly and in consequence no more fuel flows through the cross holes in the needle that the fuel well remains down slows A empty jet so until the engine or stops. handlebar-controlled air slide enrich the mixture temporarily is when provided to required. Tuning the carburetor The is throttle most which each tuning point TUNING SEshould be remembered, however, opening effective QUENCE. It is at shown under 64 Carburetors and Tuning Amal TT was developed for road racing Amal R.N. type. that a change of setting at any point some effect on the setting required For instance, a change of main jet at will have other points. will have some on the mixture strength at half throttle, which, however, is mainly controlled by the needle position. Similarly an alteration to the throttle cutaway may affect both the needle position required and the adjustment of the pilot air screw. For this reason it is necessary to tune the carbu- effect retor in a definite sequence as follows: Main The size should be chosen which speed at full throttle with the air control wide open. If two different sizes of jet give the same speed the larger should be chosen for safety as it is dangerous to run with too weak a mixture at full throttle. The pilot air screw should be set to give good idling. Note that the pilot jet is detachable (7) jet. maximum gives @ and sizes are available. If the pilot air adjusting screw needs to be screwed out less than half a turn the larger size pilot jet should be used; if the air screw needs to be screwed out more than 2-3 Amal type 27 used ^ in racing bikes. turns, fit the smaller size of pilot jet. Amal Carburetors The the one which throttle valve the correct setting of the air screw amount of cutaway which gives the fastest idling speed for a given position should be selected with will prevent spitting or misfiring when opening the throttle slowly from the idling position. The lowest position of the taper needle should be found consistent with good acceleration with the air slide wide open. (5) The pilot air screw should be checked to (3) the largest 65 if possible. When setting the adjustment of the pilot air screw this should be done in conjunction with the throttle stop. Note that improve idling is If the idling speed is then can be slowed down by un- of the throttle stop. undesirably fast it screwing the throttle stop a fraction of a turn. It be noted that of the four points at which adjustments are normally made pilot air screw, throttle cutaway, needle position and main jet size the first and third do not require changing will — — of any parts of the carburetor. Assuming that the carburetor has the standard setting to suit the particular type of engine any small adjustments occasioned by atmospheric conditions, changes in quality of fuel, etc., can usually be covered by 2. UP TO % OPEN PILOT JETS 3. '/8 TO % OPEN THROTTLE CUT AWAY adjustment of the pilot air screw and raising oi lowering the taper needle one notch. If, however the machine is used at very high altitudes or wil a very restricted air cleaner a smaller main will The following be necessary. aduction main in jet size table gives ji tr- required at differei altitudes. Altitude (ft.) Reduction 5% 9% 3,000 6,000 9,000 12,000 13% 17% In the case of carburetors for engines runnin on alcohol fuel considerably larger jets are needet. In most cases a #113 needle jet will be require*, and the main jet size will need to be increasec by an amount varying from 50% to 150% according to the grade of fuel used. If the engine is run on fuel containing a small proportion of alcohol added to the fuel, a rough and ready guide is that the main jet should be increased 1 % for every 1 % of alcohol in the fuel. Synchronizing two carburetors When fitted dure setting the slow running on machines with two carburetors, the following proce- is recommended. See that both throttle slides are open the same amount for any given position of the twist grip. This is most easily checked by looking into the air intakes while slowly opening and closing the throttles with the air slides wide open. Make (7) sure that the highest point of the cutaway on the throttle valve reaches the top of the bore simul- taneously in both carburetors. If necessary adjust one or both mid-cable adjusters in the throttle cables. © © Repeat this TO 4 OPEN NEEDLE POSITION A TO FULL OPEN MAIN JET SIZE Tuning sequence for all Amals. air slides. at a fast idle thoroughly warm. Open the air slides fully and remove the high tension lead and waterproof plug cap from the right-hand spark plug, opening the throttle if necessary to keep the engine running until A. /A procedure for the and let it run Start the engine on one cylinder. Carburetors and Tuning 66 ® Adjust the throttle stop on the left-hand carburetor to hold the throttle just wide enough open to keep the engine running with the twist grip shut. © Adjust the pilot air screw on the left-hand speed for this maximum carburetor to give the throttle position. SECTION © Slow down the engine as far as possible by adjusting the throttle stop and reset the pilot air screw the necessary to give the if new throttle position. running as maximum Repeat fast as possible AA speed for until the engine is on the smallest possible PILOT AIR PASSAGES throttle opening. © and remove the left-hand ones. © Repeat ©, © and © on hand carburetor. © Replace the left-hand plug cap NEEDLE JET Replace the right-hand plug cap and lead steps The engine should now be running -GAS SUPPLY MAIN JET the right- and lead. steadily at a fast idle. © Slow the engine down by unscrewing each If running becomes lumpy, adjust each pilot air screw an equal amount. If necessary', slow engine down further by unscrewing each throttle stop equally but do not try to get too slow an idle with a hot engine, otherwise throttle stop equally. it will be liable to stop when only partly warmed up. Dismantling and reassembling (Monobloc) After removing the carburetor, the procedure for dismantling is the same whether twin except that the twin carburetor cables are connected at junction boxes. Removal of the cable nipples from the junction boxes is quite simple and straightforward after the single cables have been disconnected from the lever and twist grip. © Remove the throttle and air slides from the body by unscrewing the mixing chamber top cap, then withdraw the slides and throttle needle. © Remove the needle retaining spring clip, compress the slide return, then push the cable nipple down and out of the slide. To release the air slide, compress the spring and slip the nipple out of the bottom of the slide. Unscrew three slotted screws and withdraw the float chamber cover and remove the float spindle bush and the float. Then withdraw the @ © Unscrew re-insert the main jet holder, until a will release the jet the banjo bolt which secures the it body. © Unscrew pilot jet. and unscrew the removed then is peg, the end of which can the pilot jet cover, All that remains to be the hexagonal locating be seen protruding within the mixing chamber. Thoroughly clean all parts in solvent or carbure- Deposits on the carburetor body are best removed by a light grade wire brush. It is advisable to wash the parts several times each in a clean quantity of solvent to avoid particles of tor cleaner. dirt remaining. Allow the parts to drain, prefera- bly using a jet of compressed air to ensure that tioned below, reassembly ing block and withdraw the banjo, instructions. Unscrew filter and junc- the needle seating block. Unscrew the tickler body; then withdraw tickler and spring. © Remove screw, then the of the body. the air jet. To jet, main Do not refit any paper washer. It is advisable to purchase replacement washers before removing the carburetor. screw and throttle stop cover nut from the bottom main jet Unscrew the main holder and needle the all from blockage. Apart from one or two points that are menis a reversal of the above fuel pipe banjo connector to the float needle seat- tion washers. few threads with a hide mallet. This block through the carburetor are engaged, then tap holes and drillings are free triangular section float needle. © Fuel flow in Amal GP. for single or jet release the jet block When replacing the jet block, ensure that the paper washer is in position; align the location slot in the jet block with the locating peg in the carburetor housing and drive the block home. Amal Carburetors Finally, note that the float spindle bush fits on the outside end of the spindle, and that the float pressure pad rests on on it. is uppermost so Float level is that the float needle marked by a small pip Inspecting the components parts liable to Ensure that the filter has not parted supporting structure, thus enabling the gasoline to bypass unfiltered. When replacing carburetor, do not overthe mesh. show wear mileage are the throttle valve © Be sure that the float does not leak by shaking it to see if it contains any fuel. Do not attempt to repair a damaged float. A new one can be purchased for a small cost. Check the gasoline filter, which fits over the needle seating block, for any possible damage to float cover. The after considerable slide, mixing cham- ber and the air slide. Inspect the throttle valve slide for excessive from its @ tighten the nuts scoring to the front area and check the extent of wear on the rear slide face. the slide should be renewed. to replace the slide If wear is slide). (D Examine the air valve for excessive wear and check that it is not actually worn through at any part. Check the fit of the air valve in the jet block. Ensure that the air valve spring is serviceable by inspecting the coils for wear. Inspect the throttle return spring for ciency and check that it has not lost and thus warp the body. AMAL apparent, In this case, be sure with the correct degree of cutaway (stamped on top of 67 GP-2 Amal. It follows the same principles as previous models but the location of the pilot jet has been changed. The remote float bowl which is a feature of this model is mounted between the two carburetors This is the newest when fitted Mk. II. to a twin such as the BSA Spitfire effi- compressive strength. Check the needle jet for wear or possible scoring and carefully examine the tapered end of the needle for similar signs. Examine inserting it the float needle for efficiency by into the inverted float needle seating block, pouring a small amount of the aperture, surrounding the needle it gasoline into and checking for leakage. GAS LEVEL LINE TO BE LEVEL WITH BASE OFCIRCLE Mounting of Amal GP on BSA Spitfire. Finding fuel level using clear plastic tube— Amal GP. 68 Carburetors and Tuning chamber relative to means of the rods on which it is suspended from its top mounting. The gas level in the chamber is indicated by a raised line on the outside of the body and in positioning the float chamber this line should be on a level with the lowest point of a circular scribed mark on the carburetor air jet plugs. The following illustration will make this clear to you and you will probably notice that with the float chamber in this position the short pipes The position of the float the two carburetors connecting it is adjustable by 12. Main 13. 15. Plug Priming button Float bowl 16. Float 14. jet 17. Damper 18. Hose 19. Idling mixture adjusting screw ring fitting 20. Throttle valve stop screw with each of the twin carburetors are straight. BING The Bing carburetor country because this it is is known fitted to principally BMW in models. Amal. Here are directions and adjustment: Disconnect intake air filter from transmission housing and remove the filter. Clean the filter element when necessary by tapping out the dust and replace it every 8,000 miles. Note: When installing the air filter, remember the locating pin and make a correct fit. Upon removal of upper engine housing cover, lift out the filter screen, clean it with gasoline and wet essentially like the It is for disassembly @ it with @ Cutaway of Bing used carburetor of parts is BMW. on Identification in text. oil. For removal and cleaning of the carburetor, unscrew the knurled ring on top and pull throttle slide upward and out. 1. Intake port 2. Feed for 3. Idling jet idling mixture 4. Plug 5. Control cable with return spring Jet needle holder 6. 7. Throttle slide 8. Air intake pipe 9. Compensating 10. Jet needle 11. Needle air feed (A) idle mixture screw; (B) idle speed screw. jet Throttle cable adjustment at handlebar. Throttle cable adjustment at carburetor. 69 Jikov Air blast (3) all passages and jets and reassem- and provided with new gaskets. For preliminary adjustment, screw the idling mixture adjusting screw fully in and then back it out one and a half turns. ble parts properly cleaned To (J) adjust the idling speed turn twist grip to idling stop position and adjust throttle cables is fastened at the end of the main jet main accessible after unscrewing the idling jet the is pilot is situated air screw. on the right-hand The located eccentrically in becomes accessible bolt after and jet bolt. side it is The above needle the throttle valve and throttle valve unscrewing the mixing on both carburetors for a play of .02". DELL ORTO The Dell Orto carburetor makes and operates is fitted most to an Amal. to that heading for information and service. Italian Refer like JIKOV The Middle-European Amal are used on JAWA versions of the faithful motorcycles. These are monobloc carburetors. The main Dell Orto carburetor. float (1) chamber cover screw, Tapered (6) float needle, (2) pipe union washer, jet Filter removal on BMW. (3) tickler retaining ring, (4) float chamber cover, (5) spring, (8) gas filter, (9) tickler, (10) gas pipe union, (11) pipe tapered needle, (7) tickler union washer, (12) pipe union nut, (13) air slide spring, (14) throttle slide cover nut, (15) cable adjusting screw, (16) cable screw locknut, (17) throttle slide cover, (18) air control slide, (19) throttle spring, (20) tapered needle anchorclip, (21) throttle slide, (22) ring clamp screw, (23) ring clamp, (24) carburetor body, left side, (25) throttle stop screw locknut, (26) pilot air screw spring, (27) pilot air screw, (28) throttle stop screw, (29) float chamber union washer. (30) slow running jet, (31) main jet, (32) float chamber union plug, (33) needle jet, (34) float chamber union washer, (35) air adjusting ing inlet, (36) float chamber, (37) float chamber cover washer, (38) float needle retaining spring, (39) float. 70 Carburetors and Tuning * o. >o -^ — O «n w l>J O o o CO en o> co no ro to ro ls» o- I O h» *» *» * I I «l «l o o o o o o : Keihin chamber By compressing top. the spring the from the recess in the throttle valve and the spring resting on the needle The needle clip secures clip can be removed. throttle cable will be freed the position oi the needle. The main jet, idling jet, throttle valve stop screw are accessible from the right-hand side of the carburetor after rescrew and the mo\ al pilot air 71 two jets has to be checked. screw should be slackened. pilot air screw should be tightened and then slackened as prescribed. After starting, the engine idling speed has to be adjusted with the throttle valve stop screw. The throttle cable play has to be taken up with the cable bolt and its position secured with the nut. jet the value of the The The throttle valve stop of the cover. for cleaning and repairing the float chamber parts is obtained after unscrewing the two M 5 screws and removing the float chamber Access top. Carburetors are adjusted at the works for breaking in. After approximately 1,500 to 2,000 km (1.000 miles) they have to be adjusted as follows: For the 2922 SB 12 carburetor (for the 453 105 (Solex) jet idling jet needle position pilot air screw For the 2924 SB model) main jet 40 (Solex) 2nd to 3rd notch from top V2 to 1 turn slack from tight 14 carburetor Honda is the big user of Keihin carburetors made in Japan. Both the slide throttle and constant vacuum types are used. The slide throttle types are fitted to all models up to the 450, which has two carburetors. A downdraft model is found on the Honda 50 Model 100-102. Accompanying illustrations make model): main KEIHIN (for the 450 the functions clear. screw (1) in pilot controls idling Turning to the right creates a richer Adjusting mixture. mixture, to the left, a leaner mixture. Screw 109 (Solex) Turning to (2) controls idle speed. the right increases speed, to the left reduces it. idling jet 40 (Solex) Idle speed should be needle position 2nd pilot air screw For the 2926 SB Vi to 12 800-1,000 RPM. from top turn slack from tight to 3rd notch 1 carburetor (for the 455 model): main 120 (Solex) 60 (Solex) jet idling jet needle position pilot air screw 2nd to 3rd notch V2 to 1 from top turn More recently carburetor 2922 SBD II has been -pmployed for the 453, 473, and 473.04 models: main jet 85 (Solex) idling jet 45 (Solex) needle position 3rd to 2nd notch from top Carburetor 2924 SBD 12 and carburetor for the 474.04 models: SBD 17B later still 450, 470, 2924 and 2924 SBD 12 2924 SBD 17B 90 (Solex) 88 (Solex) idling jet 45 (Solex) 50 (Solex) needle position 3rd to 2nd notch from top main jet Carburetor 2926 SBD 15B for the 455/05, 475, and 475.04 models: main jet 92 (Solex) idling jet 50 (Solex) needle position 3rd to 2nd notch from top (The pilot air screw setting is the same as for the SB carburetors.) This adjustment applies to gasoline of 72 octane grade (regular). The adjustment has to be checked ® for other kinds of fuel. When resetting the carburetor after running in, the throttle valve needle position has to be checked. After unscrewing the main jet bolt and the idling Keihin downdraft type is used on Honda 100102. 72 Carburetors and Tuning Fuel flow in Keihin sidedraft type. The primary function of Operation When choke lever is pushed up to full shut position, the choke (2) comes down. The relief valve (3) usually acts to shut the window (5) by the spring (4). When the throttle valve (1) is opened about Va, fuel sprays out from the pilot outlet (6) and the needle jet (7) (due to vacuum) and at the same time the relief valve (3) is opened (dotted part (8) ) properly to allow air flow through window (5) to give most adequate mixture for starting. After the engine is started, vacuum the increases, opening the relief valve (3) widely to feed adequate mixture to the cool engine. The relief valve (3) opening will vary, corresponding to the throttle valve (1) opening (9). Function of each part Main jet (10) © control fuel flow for the main jet proper mixture at is to high speed. © Air jet (5) prevent too rich a mixture at high speed (throttle wide open) or too lean a mixture at slow To speed, air is supplied to the needle jet which controls the amount. © Needle jet (4) At full throttle and at medium speed the needle jet once more works to control fuel after control by the main jet. It is adjusted at the same time as the jet needle. Jet needle (7) The function of the needle © to control mixopening (between Va and Vi turn) in conjunction with the needle jet explained above. The jet needle, having a ture ratio at medium throttle is 73 Keihin long taper, is fitted in a suspended state on the center hole of the throttle valve, the tapered end inserted in the needle jet. Therefore it moves up and down according to the throttle valve, taper responsible for adequate mixture ratio. to four positions, its The needle can be adjusted first (highest) position giving mixture leanest and fourth position giving richest mixture. The Throttle valve (6) throttle valve controls the amount of air suc- tioned by the engine and has the important function of controlling mixture. There is a cutaway on the suction side of the throttle valve. By changing the size of this cutaway, negative pressure on air amount of The range of this the needle jet can be varied to change the flow to change the mixture ratio. function is between idling and around > i turn, Adjusting float level not effective above Vi turn. Slow jet the orifice of the air bleed. Air screw (11) air screw controls the amount of ing in the idle (slow) system. air flow- controls air to It be mixed with fuel which passes through the slow jet to get adequate mixture which is forced from the end of the slow jet. In making preliminary adjustments, engine repair or replacing worn parts, be certain that each part of the engine is properly adjusted, the carburetor is checked for air leakage, all worn parts are replaced with new parts. For the full throttle is made main jet. To determine rich or lean mixture, the following procedure is used. While running at full throttle, close the choke a little; this creates a rich mixture. If the speed increases, replace the main jet with the next and check again, using same procedure. If the speed decreases when closing the larger size choke, the main jet is suitable, or too large. To determine if the jet is suitable or too large, replace jet with next smaller size. If the speed decreases and then speed increases by closing the choke, it indicates that the original jet Replace original jet is the proper one. for best performance. Intermediate speed adjustment For the opening Vs to Vi, the mixture is regulated by the height of the throttle cutaway and jet needle. Intermediate speed control is more precise since the cutaway will affect any speed under Vs throttle opening. Fuel consumption is most economical when the jet needle is leaned out to the left as much as possible without throttle left. b. If you feel the engine "braking" while constant speed, turn accelerating or running at jet needle to the right. Cutaway of throttle valve The higher the punched mark, the weaker the mixture and vice versa. Idle speed adjustment Vs throttle to idling, the mixture ulated by position (full to half open) in the causing a loss in acceleration in the intermediate speed range. Jet needle a. If black smoke comes out of the exhaust at intermediate speed, the mixture is too rich. Lean out the mixture by turning needle to the From High speed adjustment adjustment Keihin. (13) The slow jet controls flow of fuel at idling By a lower opening of the throttle a state. vaporized mixture is made by air coming through The in the air screw and the throttle is reg- valve cutaway. Air screw The mixture is regulated by the air screw while idling; a turn to the right makes the mixture richer; a turn to the left makes it leaner. After adjusting, check for engine misses by slightly opening the throttle. If there is a miss, re-adjust for better performance. Cutaway of throttle valve At almost V% throttle opening, mixture regulation is sometimes difficult. In such a case take higher cutaway number; if mixture is too rich and vice versa adjust the air screw again. Adjustment of float position (carburetor removed from engine) Place the carburetor upside down. This is not the correct float position of the regular fuel level since the spring in the float valve is retracted due to the thrust from the float valve end on the float arm by the weight of the float itself. Tilt the carburetor so that the float pin (4) stays in upper position and float ( 1 ) in lower position; hold this position just before the float Carburetors and Tuning 74 arm (3) leaves the float valve end (2) (leaving is about 70° from upside down position). Beyond a margin of 50° to 70°, the float valve (2) point does not retract. (3) Measure the height difference between the lower end of the carburetor (5) and carburetor body (6). There is no difficulty with performance if the accuracy of the float position stays within 0.5 mm (.02") up and down. If deviated from this float arm (3) by bending with amount, adjust the special care to the prescribed 0.5 mm. KEIHIN-HONDA 450 A vacuum) carburetors of on the Honda 450. With pair of c/v (constant the Solex type are used c/v type, the throttle slide is not actuated by the cable, but by negative pressure above the piston which forms the slide. The venturi is thus changed according to demand and the primary/secondary venturi relationship becomes very smooth. this directly Constant velocity carburetors are used on Honda 450. Venturi The portion of and enters is the carburetor body where squeezed by the throttle is air called it the air flow rate becomes This change in rate is accompanied by a change in pressure and if there is an opening in the side (or bottom) of the venturi section where fuel can be introduced, it will be sucked along by the airstream. To better vaporize the fuel droplets sucked up at this point, an air bleed the venturi and in higher. is used. Air bleed Air bleed is graphically illustrated by the comsoda straw. If you place a straw in your mouth and insert it into a glass of water and suck, you get a steady flow of water. If you remove your mouth from the end of the straw the water will flow back into the glass. If you make a hole in the straw, air mixes with the water and you get bubbles which show little tendency to return to the glass when you remove your mouth. If you could make an opening in the straw and introduce another straw so that the submerged junction of the "air bleed" and the "main jet" straws was under water, the bubbles in the "main jet" would be even smaller and more plentiful than previously. This is "air bleed." mon (7) Air system Air passed through the air cleaner is taken from the air intake (2) through (1) and (15). When the amount of air required by the engine small, the vacuum piston (16) is generally lowered and forms a primary venturi, thus main- is taining the flow rate in the venturi. Illustration of pressure drop in restricted area of venturi. mm (») ID) It)) (c) Illustration of air bleed principle. Keihin-Honda 450 Cutaway of Keihin constant velocity carburetor. With an increase of air volume the flow rate in narrow venturi portion ( 1 ) becomes faster the than that of the air intake (2); thus the pressure (1) becomes lower than that of the air intake (2) (i.e., becomes negative of the venturi portion pressure). The 75 difference in the pressure is trans- mitted as the pressure difference in between the upper and lower surfaces of the vacuum piston at Simultaneously, the fuel jet. from the slow jets from the is mixed with air jet at the air bleed. air The mixture pilot outlet (12) and bypass (13) near the periphery of the throttle valve. On the pilot outlet (12) the pilot screw which regulates the mixture is provided, A b. Main system part of the fuel which passes through the portion (a) and portion (b) and the force to pull main up the vacuum piston However, the other main portion mixed with air from the air jet within the air bleed of the needle jet holder, and jets out from the needle jet. When the vacuum piston (when it works as the primary is fully closed The vacuum is actuated. (16) is pulled up in a value proportionate to the flow speed, and the venturi area is increased. Further, as the engine reaches high speed, the vacuum piston rises up to the top and forms a secondary venturi sectional surface which is sufficient to maintain maximum output. (J) piston Fuel system a. Flow system The amount of fuel which passes through the main jet is controlled at slow jet through the pilot jet directed into the slow system as ex- is plained above. of the fuel is venturi) or when the vacuum piston is half closed, the tapered portion of the jet needle installed the vacuum prevent excessive fuel passage from the needle @ Float on piston squeezes the fuel in order to jet. chamber The fuel coming from the fuel tank float chamber through passage from the enters the fuel tank, 76 Carburetors and Tuning (a) Fuel flow through C V carburetor openings. at various throttle Keihin-Honda 450 77 and float valve. The float (11) is up accordingly. The float valve (6) is by the float arm (7), and when the float float valve seat floated lifted contacts the float valve seat (5), the chamber (9) is used, and the valve (6) fuel inside the float The lowered. (11) is also valve (6) leaves the float valve seat (5); thus, the fuel enters into the float chamber (6). By repeating these operations, a constant fuel level can be maintained. The lever fuel is lowered accordingly and the float float portion of the float valve (6) which contacts the float arm (7) is provided with a spring. Further, when the motorcycle is inclined or foreign matter sticks to the float valve seat, fuel overflows, and the fuel enters the cylinder; thus the overflow line Pilot jet and slow jet of C/V carburetor. has been provided to maintain the specific fuel level. When the fuel level reaches a specific level, the overflow line permits the fuel to be (8) discharged. Choke When starting engine in cold weather, it is necprovide a rich mixture and for this purpose a choke valve (3) has been provided. essary to When the choke lever (17) (3) closes and air flow However, fuel is if is raised, the is choke limited. the operation fed to the engine. For is NEEDLE JET HOLDER improper, excess this reason, a relief provided on the choke valve (3). The relief valve (18) opens and closes by the negative pressure, and makes the mixture suitable to a cold engine. valve (18) is Main jet, needle jet holder, and needle jet. GASKET VALVE SEAT Float needle valve Vacuum piston and jet needle (JN) in Keihin C/V model. components Operation of relief valve in in choke C V model. in C/V model. — Carburetors and Tuning 78 Carburetor functions © When idling, the throttle valve (15) is in an almost closed position, and the fuel is jetted from the pilot outlet (12). Accordingly, the mixture regulation performed is the pilot screw is at the pilot screw. turned Screw the needle the best engine speed in, the screw fully in is When becomes the mixture when lean and becomes rich out. may become heavy and defective. When For these reait may cause fire. tion fuel overflows, Idling is and back turned sons, the carburetor must be disassembled, inand adjusted periodically. Remove both left and right air cleaner case. Remove the 6 hex head bolt and air spected, cleaned © © mm cleaner connecting the tube latch belt, take off the left and right air cleaner covers. off until obtained with a closed throttle. © Low and cruising speeds mainly jetted from the bypass (13) because the throttle valve (15) is opened at a Accordingly, the mixture adjustspecific level. ment is set by the inside diameter of the slow jet. Note: The inside diameter is sometimes indicated by number, and for instance, if the number is #38, it means that the inside diameter is 0.38 The fuel is mm. @ Medium speed The opening of the throttle valve (15) becomes larger, the vacuum piston (16) starts rising, and from the needle jet; however, regulated by the jet needle. Accordingly, the mixture adjustment is performed by the setting position of the jet needle to the the fuel starts to jet the jetting value is vacuum piston (16). High speed © throttle valve (15) and the vacuum piston (16) are fully opened, and accordingly, the Both the jet condition needle's needle is mostly lifted out from the needle is set at the © main is that in which the up; thus, the fuel jet. is jet jetted The mixture adjustment jet. Float level adjustment measure the height of the fuel itself; thus, the fuel level is decided by the It is difficult to level height of the float. Placing the carburetor vertiand lowering the float (11) by finger, determine the position where the float valve (6) head contacts slightly the float arm (7) or clearance of about 0.1 is left between them, and then measure "H" with a level cally as shown and lightly lifting mm gage. If "H" is not the rated value, adjust it by bending the float arm (7) carefully. Note: When checking the contact of the float valve (6) and the float arm (7), it must be done very carefully, because the spring is contained in the float valve (6) and if this valve head is pushed, the spring is gone into the inside of the float valve. Carburetor cleaning and adjustment Honda 450 If the carburetor is contaminated or improperly engine efficiency is noticeably lowered. For example, if the mixture is too lean, the engine overheats, and if too rich, engine opera- adjusted, the Float level gage for Keihin. Keihin-Honda 450 79 air passage < fuel passage V/M20SC Carburetor gaseous mixture passage throttle vuU'inlet port Starter open full Starter perfectly closed p: main jet Schematic of carburetor used on Yamaha 250. @ nut, @ @ @ Loosen the carburetor belt, remove the clean carburetors with Use compressed air to clean the individual and after cleaning reassemble, reinstall, nozzles, adjust. Idling adjustment a. Turn both left the screw stop and ( 1 ) to adjust so that right exhausts are equal. the stop screw ( 1 ) is returned, if When the rotation cannot be lowered, loosen the lock nut (2), and tighten the cable adjuster (3) by one more turn. b. For either right or left, open or close the screw (4) slowly from the present position and find the position where the engine speed becomes the highest. If tightened, the pilot loosened, the mix- Readjust the difference of exhaust strength left and right which occurred with the adjustment performed in accordance with the instruction in (b) above, with the stop screw (1) in accordance with the instruction (a) above. adjustments (a) through (c) d. Repeating above, adjust the carburetors so that the proper speed and exhaust strength are obtained from both left and right carburetors. Throttle valve adjustment Adjust the throttle valve so that both side Touch both throttle throttles operate equally. arms with the fingers from beneath the carburetor and move the throttle grip a little to see if both c. and Disassemble gasoline. @ If becomes rich. The adjusting should be performed within ± Ve to Va turn. true car- buretors. and mixture becomes lean. Loosen the throttle cable adjusting bolt and remove the throttle wire from the carburetor. between the ® levers start moving loosen the lock nut adjuster (3). at (2) the same time. If not, and adjust with the cable Carburetors and Tuning Passage •*-•- of Passage Air Cutaway of of Fuel A MIKUNI Mikuni carburetors are widely used on Japanese motorcycles, with Yamaha and Suzuki as the largest customers. The chief characteristic which Mikuni is an air vent pipe and an overflow pipe so that the engine will be less distinguishes the likely to fill . . . Passage of mixture Gas Mikuni carburetor with starter on later model Yamaha. with raw fuel in case of a stuck needle valve. typical Mikuni operation is as follows: Main channel Air reaches the carburetor through the air cleaner and air cleaner tube and is inducted into from (1) through the throttle valve. This air flow creates a vacuum around the jet needle (2) and fuel in the float chamber is primed up through the main jet (3). Part of the air taken through the air jet (4) enters the needle the engine from five holes (6) located around the and creates bubbles in the fuel passing the needle jet. Air flows under the throttle valve at high speed so that bubbling fuel coming from the needle jet is atomized and mixed with the jet (5) needle jet air. Slow channel When the engine is idling the throttle valve lowered almost to the bottom, but air is taken through the air inlet (7) installed for engine idling. Air entering from the air inlet is metered by the pilot air adjusting screw (8) and primes up fuel through the pilot jet (9). A richer is Mikuni used on Yamaha 125. 81 Mikuni Phillips screwdriver and separate the float chamber from the mixing chamber. vent pipe @ @ The float can be removed from the mixing chamber body by removing the float pin. Remove the main jet with a 6 mm wrench. Remove Remove the needle jet with an 8 mm wrench. with an 8 wrench. Remove the pilot jet with a small screwAssembly is the reverse of the above driver. needle valve the seat mm sequence. Adjusting idle Turn gine (2) RPM Turn RPM the throttle valve stop screw in so enincreases. the pilot air adjusting screw in so en- Turn the screw in until the engine runs at the slowest speed. (3) After finding the lowest RPM, fix the screw a little before the lowest RPM. The engine gine decreases. RPM is still ® high at this stage. Turn the throttle valve stop screw decreases. Fix the screw at engine just before the engine stops, which should 1.200 RPM. Measure with a revolution (5) RPM Turn out within now Air vent and are safeguards 3 /4 for tF% mixture than that mixed in the main is supplied through the outlet (10) to the engine. The fuel air mixing ratio in the slow channel is controlled by the pilot air adjusting fuel/air To adjust, turn the pilot air adjusting screw to the bottom and then back the screw out 1.0 turn, which is the standard setting. Starter device or choke When the starter ("choke) lever located on the handlebar toward the rider is activated, fuel will be primed up through the starter jet (11) by vacuum in the crankcase. The fuel will mix with air in the float chamber (13) which enters from the air bleed hole (12). The mixture jets from (14) and mixes again with air coming from (15), and the new mixture jets into the main bore through the hole located in front of the throttle The mixture jets from the outlet main channel and enters the engine. valve. in the Disassembly (7) Remove four fitting screws with a small counter. of a turn and find the position channel screw. be about the pilot air adjusting screw in and pipe pipe on Mikuni two-stroke engine. overflow out and the spot Main channel of Mikuni. Carburetors and Tuning 82 where the engine runs most smoothly. justment is The ad- main jet finished. Adjusting for various speeds High speeds The mixture at 3/4 Lean ratio is adjusted by the to full throttle openings. If the engine runs turned back more smoothly when the throttle is slightly from wide open it indicates mixture throttle ture is throttle is is lean. If RPM engine closed slightly lean. is If it engine closed slightly the fuel when the drops when the indicates that the fuel mixture is correct or too rich. Use a larger numbered main jet when the fuel mixture is too lean. Medium groove indicates the fuel mix- RPM it drops n Rich speeds The mixture is by the jet needle cutaway at Va to 3A controlled position and throttle valve throttle openings. a. Adjusting with jet needle. There are five grooves in the upper part of the jet needle, and they are counted from the top to the bottom: first, second, etc. ^ 1 Typical jet needle and clip, Mikuni. 8- Throttle valve operation, Mikuni Throttle valve cutaway, Mikuni. Mikuni Removing needle valve Removing bottom of float Removing needle 83 seat, Mikuni. chamber, Mikuni valve, Mikuni. Removing pilot jet, Mikuni. exhaust fumes are white in color, it indicates Lower the jet needle is too rich. by one groove; that is, fit the clip in the second gear from the top. Third groove is standard setIf the fuel mixture ting. RPM engine is not smooth while riding and it engine brake is being applied it indicates the fuel mixture is too lean. Raise the jet needle If feels as if by one groove. A b. Adjusting with throttle valve cutaway. larger numbered cutaway increases air flow, giving a leaner mixture, and a smaller Removing main jet, Mikuni. numbered cutaway decreases air flow, giving a richer mixture. Adjusting by cutaway, however, affects engine performance at slow speeds below Va throttle opening. Do not change the throttle valve cutaway unless there is an urgent necessity. 84 Carburetors and Tuning Low speeds Fuel mixture is adjusted by the pilot air adscrew and throttle valve stop screw at and Ya throttle throttle openings between Vb openings. See adjusting idling section above. justing Overflow Fuel overflow is caused by a damaged float, imperfect contact of the needle valve and valve seat, worn needle valve, clogged carburetor fuel channel, etc. As the needle valve repeatedly contacts the valve seat to keep the fuel level correct, the tip of the needle valve is apt to wear. If the needle is worn, there will be a gap between the valve and needle valve even when the float tongue valve seat pushes the needle valve. Fuel will flow into the carburetor continuously and overflow. Check to see if the needle properly place valve contacts when disassembling the needle valve if the valve seat the carburetor. Re- needed. To check, remove the float chamber and push the float with a finger until the tongue pushes the needle valve. Turn on the fuel cock. If fuel flows into the worn. Holes in the main jet, needle jet, etc., should be cleaned when the carburetor is disassembled. Clean these with compressed air. Do not use wire, etc., to carburetor, the needle valve is clean the holes in these parts. LINKERT SCHEBLER The Linkert Schebler carburetors used for so years on Indian and big Harley-Davidson models are simple and efficient. They are also many easy to adjust and are designed to be adjusted on the road like tuning a motor scooter, which is a very productive method. The Linkert is a side draft carburetor with fixed venturi and a throttle butterfly. There are adjustand high speed jets and an idling speed screw which changes the position of the butterfly on the type used on 61" and 74" models. The 55" has a revised version which eliminates the low speed adjusting control knob and uses an idling mixture screw, and a throttle stop screw. able low speed Adjustment (61", 74") If you are starting with an engine which runs but not as well as it might, and carburetion seems to be the problem, fire it up and bring it to operating temperature. Then set the throttle stop (idling speed screw), to achieve satisfactorily about 850-900 RPM. Spark control should be retarded. Screw the low-speed needle in until the engine stumbles and almost dies. Then turn the adjuster out Va turn. Reset the throttle stop screw to desired idling speed. Harley-Davidson carburetor. (1) speed needle, (3) throttle lever, choke lever, (6) choke disc. High speed needle, (2) low throttle stop screw, (5) (4) The high speed adjustment should be carried out with the engine under load, but it can be made on the stand where the engine's ability to respond sudden increase in throttle opening is the test. advanced position and blip the throttle, opening it up suddenly, accelerating to high speed and closing it abruptly. Screw the highspeed jet needle in until the engine hesitates and dies or backfires. Then screw the control out to Set the spark to gradually, blipping the throttle until the condition ordinarily about Va turn, but in could be anything. After adjusting the high-speed jet. it will probably be necessary to reset the idle to desired speed. On-the-road adjustment is made by turning the high-speed needle control back and forth until the best acceleration characteristics from about 30 mph up to 50 mph are found. clears up. This is old carburetors it Adjustment The same 55" ) ( 55" is used for the model, but start by screwing in both the idling screw and the high-speed needle adjustment fully home and backing off \Vi turns. Fire up the engine and get it to operating temperature, with choke open. Set the idling speed at a moderately fast idle. Screw the idling adjustment in until the engine falters, then back it off enough to make the engine run smoothly. The high-speed jet is turned in gradually while suddenly accelerating the engine from idle to high speed. When it begins to stumble and backfire, general idea 85 Zenith hands of past owners or meis the result and all the twiddling in the world won't bring them into adjustment. Check with an oil can filled with tightening in the chanics. Air leakage gasoline, i.e., squirt fuel at the flange base with the engine idling. If the engine speeds up, you've got an air leak. Overhauling Disassembling and cleaning of any of these carburetors follows an obvious pattern, with attento be paid to the following points on reassembly: (7) Be sure the venturi is installed properly with the main jet well (spray nozzle) projecting into it, and the small spring placed under it. tion @ The stepped washer below needle spring is critical. the low speed If left out, too much air can be vented past the needle and the mixture will be too lean and make low speed difficult to adjust. Float level is approximately lA" from top @ Bend of float to top of bowl. the float lever carefully between the float and the fulcrum pin, preferably with the float removed from the bowl to avoid bending the small prongs which contact (1) Carburetor body, (2) mixing chamcable adjuster, (4) adjuster locknut, (5) throttle slide, (6) slide spring, (7) top to body screw, (8) starter slide, (9) throttle stop screw, (10) stop screw spring, (11) clamp nut and bolt, (12) plug screw, (13) emulsion tube, (14) main Zenith carburetor. ber top, jet, (15) slow running washer, (19) jet, (16) float, (17) float hinge pin, bowl screw, (21) feed pipe, (22) union bolt, (23) fiber washer, (24) fiber washer, (25) filter gauze, (26) intake adaptor, (27) adaptor screw, (28) shakeproof washer, (29) rubber connection, (30) throttle cable, (31) adaptor to head, (32) "0"-ring, (33) air filter. (18) joint the needle head. (3) float bowl, (20) float turn the needle back out just enough to enable it." You can check this on the road by accelerating from 30 to 50 mph. The big problem with many of these carburetors is warpage of the flange caused by improper bolt the engine to "take ZENITH Zenith MX carburetors Triumph models. This is a accompanying illustration are used on slide-throttle type. will make some The the disposi- tion of parts clear. There is no float tickler, but pressing down the plunger (8) to the limit of its travel will provide a rich mixture for starting when cold. The metering hole in the plunger mates with an air passage in the body and fuel is drawn through the slowrunning jet (15). After a short time (30 seconds or so) open the throttle to the full extent to return the plunger to its normal position. 86 Carburetors and Tuning TDC TUNING is taken out of exhaust pushrod valve clearance. Adjust the point gap. Use a pair of feeler gages in the same way as for the valves. Points are on spring tension and they can easily be forced and were known, most motorcycle enfrom inept tuning. Because the cycle engine is so simple in format and so accessible, nearly every rider, at one time or anIf the truth gine troubles stem other, undertakes to "tune it up." This isn't bad, in fact it is commendatory. But too few of them attempt to find out anything about the process before they begin. No good mechanic ever picks up a screwdriver in anger unless he has access to the right information about the machine he is approaching. Amateurs should be as conscientious. Tuning consists of adjusting the variables so that they meet factory specifications, as far as street bikes are concerned. Racing is another matter, which doesn't concern us here. The four-stroke variables are and play set intake © open with the gage. @ © © © the © (J) Set the ignition static timing. Re-check the point gap, just to be sure. Check the automatic advance with a timing light. Clean, adjust, or replace the spark plug. Make sure the throttle twist grip is is opening fully when wide open. Start the engine, warm it up, adjust the idle speed screw to give a moderately fast idle. Screw the pilot needle (slow speed screw) in until the engine starts to stumble and back it off Vs to Va Twist the throttle open abruptly. If it turn. valve timing, ( 1 ) (2) valve clearance, (3) fuel/air ratio, (4) spark timing, (5) point and plug gap. Two-stroke mechanics have even about: carburetion, spark timing, deal, if you go less to worry and points, plug. So tuning is no big at it logically. arm, lifter, etc.) clearance. This is specified with engine cold in almost all cases. "Cold" simply means that the engine should be approximately the same temperature as the rest of the bike, the frame, etc. In other words, don't adjust the valves if the engine, or the oil in the engine, is warmer to the touch than any other part. Letting it sit overnight is the rule followed by most shops, but whatever time it takes to cool down is the amount to allow. Clearances specified with engine warm are marked with. an asterisk (*). The best way to gage the clearance is by go (?) Set the valve/tappet (rocker Establishing top dead center with steel ruler. and no-go. If clearance is specified as .008", don't check it with a .008" feeler gage. Use a .007", which should slide through the space, and a .009" which should not. The most important thing is to be sure you have the tappet, pushrod, rocker arm (or whatever is applicable to the type of valve train in your machine) on the heel of the cam, and not slightly onto the quietening ramp or the lobe itself. This means that you should have the piston at top dead center on the compression stroke, not the exhaust stroke. At this point you can set both inlet and exhaust valve clearance. This does not hold true with the Triumph twins and Matchless singles, however. On the Triumphs, set clearance on the intake valve of one cylinder when the intake valve on the other cylinder is fully open, then repeat with the exhaust valves in the same manner. On the Matchless, rotate the engine until the piston is at TDC on compression/ ignition. Turn the engine back until play is just taken out of intake pushrod and set exhaust valve clearance. Then turn the engine forward until past Later BSA models have crankcase plug automatic advance. to define limit of 87 Tuning Ariel MODEL 50-75cc PLUGS POINTS TAPPETS Exh. Int. .020 .012 .003 .003 020 .014 .010 .012 250cc Arrow & Leader .030 .015 350-500cc singles .015 .018 .012 .006 .008 500cc twin motor .015 .018 .012 .005 .008 650cc twin .015 .018 .012 .010 .010 lOOOcc 1949-52 .018 .020 .015 .001 .001 1000CC 4-Port 1953'59 018 .020 .015 .006 .008 Pixie 200cc Colt BMW MODEL PLUGS POINTS TAPPETS Int. Exh. .008 R 50 .024 .016 .006 R 50S .024 .016 .006 .008 R 60 .024 .016 .006 .008 R 69S .024 .016 006 .008 BSA MODEL PLUGS POINTS 75cc Beagle Starlite .020 .012 125-150-175cc Bantam .020 .015 250cc C1 C12 1947*48 TAPPETS Int. Exh. .003 .003 .020 .014 .012 .012 250cc C15 1959-'64 .020 .015 .008 .008 350cc B31 .020 .012 .003 .003 500cc B33 .020 .012 .003 .003 500cc B34GS .020 .012 .006 .006 500cc A7 1951'62 .020 .012 .008 .010 500cc A50 twin 1962'64 .025 .015 .008 .010 1, 650c c A10 .020 .012 .008 .010 650cc A10R .020 .012 .008 .010 650cc A65 .025 .015 .008 .010 650cc A65R .025 .015 .008 .010 500cc A501R .010 .023 .015 .008 A502W .023 .015 .008 .010 650cc A652H .023 .015 .008 .010 650cc A652L .023 .015 .008 .010 650cc A651T .023 .015 .008 .010 650cc A65SP .023 .015 .008 .010 441cc Enduro .023 .015 .008 .010 500cc Harley-Davjdson MODEL PLUGS POINTS TAPPETS Exh. Int. '55 XLCH .025 .022 .001 .002 74 S.V. .025 .022 .005 .007 .001 61-74 ovh 1936-47 .025 .022 74 ovh 1948-'64 .025 .022 125-165-175 .020 .015 .002 Hydraulic 88 Carburetors and Tuning Kawasaki Greeves MODEL MODEL PLUGS PLUGS POINTS 24 MX2 250cc .026 .016 85-J1I .026 .015 TE 250cc Trials .026 .016 85-J1TRI .026 .015 TES 250cc Trials .026 .016 100-D1 .024 .015 24 RDS .026 .016 125-B8T .026 .015 250cc Sports Circuit Racer .026 .016 175-F1 .026 .015 175-F2 026 015 250-A1 .026 .015 POINTS Honi 3A MODEL 50-55cc PLUGS POINTS TAPPETS Int. Exh. .004 .026 .014 .004 90-S90 .026 .014 .002 .004 125cc mod. C92 .026 .014 .004 .004 .004 (All) 150cc mod. C95 .026 .014 .004 125cc mod. CB125 .026 .014 .004 .006 160cc mod. CB160 .026 .014 .004 .006 .004 250cc mod. CB72 .026 .014 .004 300cc mod. CB77 .026 .014 .004 .004 450cc mod. CB450 .026 .014 .012 .012 Indian MODEL PLUGS POINTS TAPPETS Exh. Int. 500cc 30.5" .020 .015 .005 .008 750cc 45" .020 .015 .005 .008 200-1 300cc 74" & 80" .020 .015 .005 .008 250cc Brave .025 .018 .003 .004 438cc twin .025 .015 .003 .003 220cc single .025 .015 .003 .003 500cc twin ovc .025 .025 .003 .003 1 Matchless & MODEL PLUGS A.J.S. POINTS TAPPETS Exh. Int. 250cc .020 .012 Nil* Nil* 350cc .020 .012 Nil* Nil* 500cc .020 .012 Nil* Nil* 500cc "CS" .020 .012 .006 .006 600cc "TCS" .020 .012 .006 .006 500cc twin .020 .012 .006 .006 600cc twin .020 .012 .006 .006 650cc twin .020 .012 .006 .006 Norton MODEL PLUGS POINTS TAPPETS Int. Exh. 400cc .020 .012 Nil Nil 500cc .020 .012 .004 .006 600cc twin .020 .015 .002 .005 650cc twin .020 .015 .002 .005 750cc twin .020 .015 .006 .008 500cc twin .020 .012 .002 .005 89 Tuning Panther MODEL PLUGS POINTS TAPPETS Int. Exh. 250cc .020 .014 Nil Nil 350cc .020 .014 Nil Nil 600cc .020 Nil* Nil* 650cc .020 Nil* Nil* Royal Enfield TAPPETS MODEL PLUGS POINTS (Aluminum Head) Int. Exh. 250cc Crusader .020 .015 .002 .004 350cc Bullet .020 .015 Nil Nil 500cc Bullet .020 .015 Nil Nil 700 & 750cc twin .020 .015 Nil Nil 750 Interceptor .020 .015 .003 .005 Sunbeam MODEL 500cc S7 PLUGS S8 POINTS .020 .012 TAPPETS Int. Exh. .018 .018 Triumph MODEL PLUGS Standard T20 POINTS TAPPETS Int. Exh. .020 .015 .010 .010 .020 .015 .002 .004 350cc 3T .020 .012 .001 .002 500cc 5T .020 .012 .001 .002 500cc T100, Tiger 100 .020 .012 .002 .004 650cc 6T, .010 Sports T20S & T20SH Tiger 110 .020 .012 .010 350cc 3TA Twenty-one .020 .015 .010 .010 500cc 5TA Speed twin .020 .015 .010 .010 500cc T100A Tiger 100 .020 .015 .002 .004 500cc T100SS Tiger 100 .020 .015 .002 .004 650cc Third 6T 1955-62 .020 .015 .002 .004 TR6 Trophy 1955*62 .020 .015 .002 .004 T100 Tiger 110 1955*62 .020 .015 .002 .004 T120 Bonneville 1955*62 .020 .015 .002 .004 .020 .015 .002 .004 TR6 Trophy 1963*64 .020 .015 .002 .004 T120 Bonneville 1963*64 .020 .015 .002 .004 T'bird, 6T Thunderbird 1 963 64 Velocette MODEL PLUGS POINTS TAPPETS Int. Exh. .006 200cc twin LE .020 .012 .004 350cc ovc .020 .012 .005 .005 500cc ovc .020 .012 .005 .005 90 Carburetors and Tuning Monte sa MODEL Suzuki PLUGS 175cc Impala Sport .012 .016 175cc Enduro .012 .016 1 75-250cc Impala Cross 250cc Scorpion MODEL POINTS .012 .014 .012 .012 All models 1000cc Rapide 1 MODEL 98cc 1, 2, 4, & 6F 125cc 10D & 12F 150cc 31C 200cc 6E, 8E, & 9E 250cc PLUGS POINTS .025 .015 .025 .015 .025 .015 .025 .015 .025 .015 stumbles, richen the mixture slightly. Then POINTS .024 .014 PLUGS POINTS .018 .012 .018 .012 PLUGS POINTS .024 .014 Vincent MODEL VlLLIERS PLUGS 0OOcc Black Shadow Yamaha MODEL All models re-set speed as you prefer it. This should make the bike run as well as its condition will allow. To go any farther than this, check the appropriate heading in the carburetor chapter for the finer points of individual carburetor tuning. If you have a two-stroke, ignore the valve timing bit and proceed through ($). idle ADJUSTING FEELER SCREW GAUGE @ FIXED CONTACT PLATE SECURING SCREW 0-OI2-OOI5 SCREW DRIVER Chapter 6 Frame and Running Gear Troubles associated with the frame and running show up as excessive tire wear, poor steering, inferior braking, or bottoming of the suspension. Also to be included under this general heading would be the effects of too much or too gear generally little chain tension. Abnormal overloading If wear tire Improper cycle ARK inflation is is the principal curse of tires; the second offender. you do not have the owner's manual for the (or in case the owner's manual fails to supply information because some Japanese the printer left the information out) here thumb guide to minimum is a rule of Balance mark on inflation. Front Rear 2.25 2.50 22 20 2.75 16 3.00 3.25 3.50 17 28 26 22 22 Tire size 15 Misalignment 2.75 225 275 325 350 150 175 3.00 3.25 3.50 wear. Check Loose or bent spokes can pull a rim out of true and lots of riders whip out the old spoke wrench and go to work. You can do it, but the best advice is to take the wheel to somebody who has plenty of experience. Each spoke must be tightened or loosened a fraction of a turn at a time and it is a time-consuming process. The tyro is apt to pull the wheel out of round while trying to cure this: Weight tire Wheel-trueing Generally the lightest bike to with each size tire goes something like Size 2.25 2.50 cause or the rear wheel removed for any reason. increase pressure. fitted will also the the alignment of the wheels with a long straightedge, particularly if the chain has been replaced These standards would be for the lightest bike and lightest rider. As you add weight you must be should be adjacent to valve stem. Over-inflation results in excess wear in center of the tread, hard, jolting riding, etc. 21 16 17 & up tire lateral deflection. Heavy or stiff steering In addition to low front tire pressure, which seems pretty obvious, heavy steering can be traced to bad steering head bearings or incorrect adjust- For every 25 pounds of unladen weight over add a pound of air to front and rear. For every 25 pounds you weigh over 150, add a pound, front and rear. If you are going to carry a passenger, add about 5 pounds to the rear and a couple to the front. For sustained high speed riding, higher pressures than normal are bearings in the steering head or in the first choices in this case. In the case of non-adjustable bearings, replacement required. is these standards, ment of Uncertain or wobbly steering Worn front wheel are the This will prevent you from ruining tires by under-inflation and will assure fairly decent handling. To get exactly the right combination for your cycle is a matter of trial and error, however. The symptoms of tire wear mushy under-inflation are poor handling, the natural course. Another possibility is that not properly seated on the rim, not running true. This latter condition will show up as the tire is handlebar oscillation at slow speed. Bottoming of suspension excess at the sides of the tread (plus, of course, steering, the control. In the high mileage bike this can be due to fatigued springs, but etc.). 91 more than likely it is caused Frame and Running Gear 92 Damper lock spring setscrew Steering damper knob Steering damper lock spring on spring Front fork top bridge er case Steering stem Installation of rear cushion, typical. Steering damper plate Steering damper friction disc A Steering damper plate 3 ADJUSTER Steering damper spring Steering damper spring nut Steering damper spring nut ADJUSTER "~ LOCKN sT^T. Steering damper cutaway, Honda 450, typical of other models. Front brake ing indicates adjustment, Triumph. The dotted line drawof the brake lever when linings are position badly worn. STEERING- Removing steering stem, downward, Honda. by lack of oil in the front forks and/or failure of the shock unit in the rear. The oil in front forks should be replaced at 10,000 miles or seasonally. If this is not done, gumming and deterioration of the oil can result in poor action. Rear cushion units should be replaced as a unit. Although "Spindle Oil" is the term used by many factories in describing the oil to be used in forks, any good lubricating oil can be used. SAE 30 is generally the grade in summer or in climates where winter temperature doesn't drop below 56° in the daytime. In the winter in rough climates, ADJUSTER NUT Rear brake adjustment, lever Triumph. shows position when Dotted line drawing linings are worn. of Frame and Running Gear Rear cushion upper case Rear cushion / / spring seat stop Rear damper upper / Rear damper seal retainer | Re Rear cushion rebound stop Rear cushion stop ^ 93 cushion bottom case Rear damper valve Rear cushion spring adjuster joint complete Rear dmper rod 1 / W Rear dan valve S «>P\ \ Rear damper rod guide Rear dam P er lnner P'P e Rear damper piston Rear damper Rear cushion spring oil seal Cross section of rear cushion assembly, Honda 450, typical of other models. Front Fork Drain Cock Boll Front fork cushion, Honda 450, typical of other models. SAE 10 can be substituted. For some riders yearround 20 weight is satisfactory. It doesn't cost much to experiment and the handling of the bike can be tailored a great deal to your liking by changing the oil. Some mechanics suggest the use of non-detergent, or low detergent such as Valvoline. about replacing the shoes, because the brakes lose quite a bit of effectiveness when hot. Most models have lining measuring approximately %" thick when fresh. Chain whining This stems from be a warning Dragging brakes causes It should because excess tension a too-tight condition. to the rider chain and sprocket wear plus wear on Externally, lack of free play in the brake pedal hand lever will cause dragging brakes. Internweak return springs or rusted cam and lever shafts can prevent full retraction. The symptoms or ally, may not be so severe as to include poor perform- ance, yet there can be enough drag cessive brake lining wear. is to cause ex- The obvious symptom hot wheel hubs. Scraping sound from brakes This due to worn-out brake broken pivot. is shoe, or linings, a broken Lining replacement time This comes when lining thickness is half-reduced. At this point the adjustment is pretty well taken up in most bikes. When half the adjustment has been used, it is a good idea to begin thinking Removing front fork caps for wheel removal, BSA. Frame and Running Gear 94 TRAILING, SH OE l LEADING SHOE ^^Jy Stretching chain to determine amount of wear. bushings and bearings in the transmission case, which leads Shoe arrangement for front brakes, BSA. to stripped gears and all sorts of good things. Chain flopping Rattling, slapping sounds signify excess slack. This is as bad as too tight a chain as far as sprocket wear is concerned and the intermittent shocks to the rest of the drive train don't do it any good either. Chain adjustment Proper chain adjustment usually calls for Vi" A" of slack halfway between sprockets with the machine on its wheels, unladen. to 3 Chain tips wash job, Use a medium weight oil with Molykote or some similar molybdenum disulfide additive. A worn chain can wear the sprockets by rising up and down. A worn sprocket Oil the chain once a week, after every Cross section of rear hub, Honda 450. and after riding in the rain. can ruin a chain. Replace the whole set when wear is evident. To determine if a chain is worn, remove it and hold it out parallel to the ground to check sideways deflection. Wear of up to lA inch per foot is permissible inasmuch as this can be tolerated before the surface-hardening of the bearings is worn through. if the chain is serviceable, remove it, clean it thoroughly in solvent. Drive a nail in a To check fiat hook a link of the chain over it, and out as tight as possible. Here are the surface, stretch it tolerances for various chains to be measured against a ruler. Cross section of front hub, Honda 450. 5/s" Chain driving direction pitch 10 7/3 2". Vi" pitch 16 pitches equals 10"; maximum: 23 pitches equals WVi"; maxi- mum: 11%". %" pitch 24 pitches equals 9"; maximum: 9%e". When Chain master link. Be sure closed end rotation. is in direction of installing the chain, of the master link rotation. is be sure the open end away from the direction of 1 1 im $4.95 CHILTON'S by OCEE RITCH A comprehensive Guide locate to assist the motorcycle owner or mechanic to the defective unit before he begins any disassembly. enable you to pinpoint the trouble so that you for as you are disassembling the time and money In addition, in making any will Therefore, unit. know what it It will to look will usually save repair. there will be times when a motorcycle is stalled far from any repair shop with testing equipment. Included are some simple tests to locate the trouble This Guide is and get the engine started. organized around the familiar units of the motorcycle: both four-stroke and two-stroke engines, fuel system, electrical system, and frame. found in Included also are valuable tuning tips which cannot be any shop manual. Illustrated with step by step photos, ical and exploded views of the mechan- electrical units plus a selection of wiring diagrams for the more popular models of motorcycles. CHILTON BOOKS A Division of Chilton Company Publishers Philadelphia and New York M