Originally Posted by
defcon13
im experiencing something with my go engine (.21 5 port turbo, not the gx serie) and i want to know what can cause this. first ,the engine has about 3.5 gal and the pinch is excellent. i dont know why, but the idle is irregular. coming from few laps on the track, it idles slightly high (for 3-4 sec) then slows down to normal idle. but then after few seconds, goes up again for few seconds, and down again, and it keeps this pattern. the tuning seems right on and temps are good.one of the guy at the track told me to add another head shim (but instructions sheet for the engine says its shimmed for 25%-30% fuel). im currently using 30% fuel (byron) with stock shimming. and im using os p3 plugs. its the first time i see this kind of behavior from a nitro engine. anybody have an idea of what can cause this?
So the engine ran fine for three and a half gallons of fuel,
then started the strange idle? I don't think any shim change
is going to fix your problem. Have you checked the front bearing,
fuel tank and lid, fuel lines, carb needles for leaks. I had a small
peice of h.s.n. o-ring floating around inside a carb one time.
Blow some fuel into the carb with th h.s.n. removed. I bet
you'll see some small chunks-o-shat float out the top of the
h.s.n. housing.