I am having some problems with my 30cc homelite . It is only turning at 5150rpm with a 18x6 prop. I have installed a bigger carb velocity stack and pitts muffler. My muffler does not have a nipple on it yet for back presure to the tank do not know if that helps at all or not. I runs very consistent no pulsing or stutering. also when i tried to fly inverted the motor stalled out imediatly no stutter just shut right of could that be because of the lack of back pressure to the tank i checked the clunk in the tank and it is ok. the motor is also mounted on the plane staight up plug on top. I am to undestand that it should tach out at high 6000 or low 7000 rpm on that size prop. Any help would be greatly appreciated.
thanks again
aaron

You don't need muffler pressure, the carb pumps it's fuel, and it doesn't make any difference which way the engine is mounted. You should be getting about 6800 rpm with an 18-6. Maybe check your needle settings again. 1-1/2 turns out on both needles is a good place to start.

Jim

That's right, no muffler pressure. Are you sure you have the fuel line connected to the correct tube on the carb, and the other tube blocked off? Something's wrong here for sure. It should run just fine inverted, and my 25cc turns an APC 16 x 6 prop at 8500 +. Yours should have more power than mine. If this was converted out of an engine that had laid around for a while it very well could need the carb cleaned and/or rebuilt. Timing set correctly?

Good luck and let us know,
AV8TOR

That's right, I forgot about the tubes on the carb. You should block the one that feeds the primer bulb. You can just put a piece of tubing on it and plug it. Once you determine for sure which one is the primer tube you can crimp and solder it if you want to.

Jim

Make sure the pulse hole on the carb lines up with the one in the head and is not blocked by the gasket, else the carb wont pump.