Hey guys. As you can see above I've been playing with the stock CAG carburetors but last night I got talking to Sol about the walbro's and started getting some ideas that might be worth trying.
When I was running the walbro on my stock 39cc fuel delivery was great and I could easily max out my bike. Same deal when i tried it on the 39cc with bolt on go fast bits. But when moved over to the modified 49cc the good times ended. I was experiencing mid range fuel surge at full throttle and at the top end out right lean out condition if I was unlucky or extreme stuttering like a rev limiter where power would come on off on off on off. I thought it was too harsh to be reed flutter.
Another tell tail sign of the problem I'm about to mention is that on both my walbro rep and genuine carbs I couldn't possibly over richen the high speed needle to the point where I could experience a performance loss. The screw needles would wobble and fall out long before you got there.
Can you see a pattern forming ? Fuel starvation.
After doing a little reading and trying to understand exactly how the pumper carburetors work I came across this little gem of a site.
http://www.aerocorsair.com/id28.htm which confirms my suspicions. If what is said in the article is correct then I would hazard a guess and say this is my problem.
If i can get my hands on a pressure tester for cheap I will give it a go using the standard spring then substitute for another spring that I can modify.
p.s I think a better configured pressure pulse hole would really help a lot for this problem too as you need a clean vacuum and pressure pulse to make the carburetor work.
Discuss....
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