Tuning the 50cc two Stroke in the Motobecane

Published on 1 October 2023 at 15:05

With the engine running I did a few other minor jobs eg made a couple of cables and a decent earth lead for the engine I thought it would be a good idea to see if I could get it running better.

I knew I had a consistent spark and that my ignition timing was as close as I could get it but it just wouldn't pick up from idle and had no power a the bottom end. My immediate thought was a carb problem, but with the mix of parts and lack of technical info there are plenty of other variables too. Just for a laugh I thought I would see what would happen with the exhaust removed, all that achieved was several hours of deafness and a Wife wondering what the hell all the noise was about. It certainly made matters considerably worse in the running department.

With the exhaust back on I had a further play with ignition timing but where I had it originally seemed to give the best results. I took the carb apart and cleaned it but all the jets were clear so thought that was all best left alone. I decided while I had it apart to try the needle at a different height - it was one notch away from the highest eg richest setting so I tried dropping it down a notch, which made matters noticeably worse. This was a good thing as it strongly suggested that moving the needle one notch up would therefore make matters better, which it indeed did. It is now running better than I have had it thus far, it will even pull away with me on the bike now. It's still not right, I think I need to make a basic air filter for it, which will richen things up just a wee bit and it should be pretty close then. It ticks over better now, the mid range pick up is significantly improved, I feel I am on the right path.

The other thing I want to try is raising the barrel another few thou with a thin gasket, I have a feeling a slight change in port timing may be beneficial - I don't want to start porting, I'm pretty sure that would have been done already by Dr Joe's team. I know the bike produced over 6 bhp with the parts it now has on it, I'm convinced it's just a matter of fine tuning now. It absolutely screams at the top end, as soon as I have sorted out the minor bogging I will connect up the front brake and give it a proper test ride.

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