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Home made magneto for a Honda CB450

This article has been sent to me by Axel! Thank you and I will soon process the other article as well, regarding a modyfying a Honda 175! The article's author is Gordon Jennings and dates from December 1969. I cannot tell where this has been published because the source has not been mentioned.

For about $30, and just a few hours of your time, you can rid that bike of its battery with an efficient, reliable... HOME MADE MAGNETO

Article by Gordon Jennings, December 1969

One of these years I'm going to tire of playing Don Quixote to Jess Thomas’ Sancho Panza. Jess very sensibly prefers to spend his time maintaining and fine- tuning factory-built racing bikes; I am always tilting windmills by creating my own racing equipment from a touring-motorcycle base. Predictably, Jess gets a good ride at nearly every race while I struggle with a seemingly endless sorting-out process. Still, all the problems and aggravations notwithstanding, I will probably continue, battling the windmills simply because there is so much to be learned in do-it-yourself.

At this time last year, | began work on a new bike for the 1969 season: a Honda CB450-based road racer. My reasons for selecting this particular bike were one: it offered considerable potential, with double overhead camshafts and a five-speed transmission, and two; it was known for having a high degree of reliability. It was available (we had obtained one for a road test) and I thought it was about time for another try with a four-stroke engine after so many months with the window-valve wonders.

When embarking on a project of this sort, a lot of fundamental decisions must be made as to the shape things will take. But in this instance, most decisions had been made for me by others. The AMA rules require that near-standard frame and forks be used—unless you can get approval from those who manufactured your motorcycle to substitute. Honda has never approved anything but Honda equipment except for brakes, and I knew that the frame and forks that came with the bike would have to suffice, for better or for worse. Honda did, however, approve installation of a Fontana four-shoe front brake. I found that the tank, seat and fairing made for Hartley-Davidson’s KR would fit the Honda—although it was necessary to make a new bottom for the tank to fit down over the Honda frame. All the rest would be Honda, slightly modified.

This gave me all the basic hardware. It was still necessary to work out the details for the various systems, like carburetion and ignition. This last was most bothersome, because while I did not want to carry a battery on the bike, there was no magneto available that would fit without a lot of machining. The lads at Precision Machining had faced the same problem when building their very successful 450, and had ultimately used a Yamaha magneto—which required the fitting of special seals and cutting a new taper on the end of the Honda crankshaft.

One of the primary reasons PM had for going to that crankshaft-mounted magneto was to dispense with the stock Honda points and breaker-cam setup. They had used a standard battery/coil system, and found a serious misfire up in the 10,000 rpm range that would not go away, Changes in coils, and condensers, and points had no effect; the misfire was still with them. It was eliminated when they switched to the magneto.

But for all the machining required, I might very well have done the same. Unfortunately, I didn't have that much time to devote to an ignition system; an alternative would have to be found. The question was: what alternative? It was obvious that I could not expect good results with the standard ignition system. PM had tried that without success, and I knew that my CB 450 would misfire like mad if taken past the 9700 rpm red line, And there was my clue: it seemed just a little too pat that the misfire would occur so near the red line; perhaps Honda had built in the misfire ...

Unfortunately, the rest of this article is missing. Do you recognise this article and do you happen to have the full article? Please send it to me!

home made magneto honda cb450 page 01


0 #1 Blue2swing 2020-04-27 09:24
This is from Cycle Magazine Dec 1969

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