Converting a CF70 to 50cc

[George Crookston]

Has anyone converted a 70cc CF70 to 50cc, is it just the barrel and piston that has to be changed?

[Peter van Geelen.]

Hi George and welcome!

If I rely on my knowledge of an SS50 engine, it is indeed a matter of changing the barrel and piston.
But to be sure, I will have to dive into my documentation and will get back to you! ;)

[George Crookston]

Thanks Peter

[Peter van Geelen.]

My 1973 parts list confirms that the connecting rod and the crankshaft of the CF50 and CF70 are similar. The crankshaft is somewhat odd due to a minor difference but this does not influence the stroke. (That's what she said)

So you can just replace the barrel and piston and all should be fine. But please keep in mind that the cylinder head of a 50cc is different from a 70cc. Perhaps it works, just try it out carefully. Also, the carburetors also are different in regards to the gauge and jet sizes. The main jet of the CF50 is 55 and it is 70 of the CF70. I was hoping to have a CF workshop manual, but unfortunately I have not, so I cannot tell you what the gauge is of the carburetors.

I hope this helped and if you need more info, feel free to ask and check out http://download.4-stroke.net for the parts list! :D

[George Crookston]

Thanks again Peter, that makes life a bit easier. I was thinking about buying a complete C50 engine unit to swap over. The traffic laws in the UK allow me to drive a moped on my car license without L plates and no need to keep taking the CBT every 2 years, I did not realise this when I bought the CF70 a couple of years ago to put in my motorhome garage. I've looked at a few scooters since but they all weigh more than the Honda.

[Peter van Geelen.]

Thank you George! ;)

And it should be no problem to fit a complete C50 engine under the CF70 and it may as well be a lot easier to do!

What does CBT stand for? All i can find is "Cognitive behavioral therapy" but I don't think that's applicable to driving a light motorbike?

The law here is the same, if you have a drivers licence, you can drive mopeds up to 50cc. Anything over that requires a motorbike licence. I'm secretly hoping for the day that one can drive a light motorbike (say, up to 125cc) with just a car licence, like they have in Germany. But I think that will never happen.

[George Crookston]

Hi Peter
The CBT is the UK Compulsary Basic Training requiered for over 50cc if you passed your test after 2000

Regards

[Peter van Geelen.]

Ah okay :grin: