cutarug

I converted a Huasheng 139F39cc 4 stroke engine and I get 6000 rpm with a Bolly 21 x 8 , but need a bit more performance, even 200 RPM would do it.
The engine is reliable and does not overheat like Saitos's and alike and run on straight petrol.
Are there hot ups I can do to get some more performance.

kamlooper

My Feedback: (1)

What do you have for exhaust? Try a different carb?
Find av8tor1977's pthreads on here and read up, Quite a bit of good info to be had. He doesnt post here much anymore though.

cutarug

I tried a 2 stroke walbro No24 and used crankcase pulse for pump but it could not deliver the fuel required so went back to original carb
Exhaust is a short pipe 50mm long.
I have 3d printed a new cam in ABS with higher lift and longer duration but have not tried it yet.
Yes av8tor1977's posts are full of good info especially with Ryobi , 2 strokes.

Tidnab

My Feedback: (51)

What kind of carb is on it ? Is it a rotary or diaphragm and what number is it ? I usually get more rpms by using a bigger venturi carb,but not too big.

1967brutus

If anything, I would first check whether all parameters are in order, like valve clearance and ignition timing, mixture strenght and such. Because 6000 RPM on a 21 x 8 indeed seems a bit low to me.

I am a bit amazed about the 3D printed cam, I don't think ABS will last very long, to be honest.

You do not give info on what the original carb is, and whether it has adjustable jets or needles or not, what kind of venturi diameter the original carb has vs the Walbro you tried, so it is difficult to assess the situation from here.