I have a 3.1c.i. (51cc) Sachs chainsaw conversion that I am having problems with. It seems to run pretty good, but is missing quite often. It only happens at mid to high throttle. I have a CH ignition with synchrospark. I am also having a problem with it loading up and dying when I advance the throttle from an idle. I have leaned out the low needle but it doesn't seem to help. If I keep it around 3K and above it does not have a problem, but if I let it idle for more than 3 seconds it will not transition. Any pointers? It was only swinging a 21x10 at 6200rpm. I later tried a 20x6 that a friend had. It was turning 8400rpm. I was thinking it should have turned the 21x10 much higher.

Try looking for air leaks aroung the carb. Did you try going richer, are you sure it's loading up and not going lean?

I have found that a poor idle to max throttle response is most often caused by being to lean not being rich. What I have found to work when adjusting carb settings is to adjust the high end, then I bring the rpm's down to a lower range (1/3) throttle and adjust the low jet so the engine runs smooth, then check my throttle response. If I try to adjust the low end at idle it seems to cause problems in the low to mid range. After you get the low end set check your high end again, and repeat if need be. I use my throttle servo to set my idle.

Well I tore into my setup and did find 1 problem right off. My timing was set at 41 deg full advance. That would explain the poor performance on the 21x10 prop. I have readjusted it, but have not gotten a chance to tach it again. I will try it later and see what happens.

Mark