DougT and I have be talking about this off and on for a bit now. Seems that the ryobi 4-stroke needs a special carb because of the way the vacum works the carb. Its been said that no other carb other than the one that comes with it will work right. I havent got mine running yet so I cant test that theory but I havent heard anyone else that has tried a different carb on it yet either. Untill I can verify it one way or another for myself I still believe a carb change would do the motor good. There might be a simple work-around to get any carb to work on the motor out there, I just got to get testing as soon as I can get a mount for it. Piper