predator500: You may have to check the reed valve to see if its clean and not bent. It acts like a one way valve allowing fue/air mix to enter crankcase on up-stroke of piston. On downstroke it has got to close so the air/fuel mix will not flow back out carb and travel through by-pass ports into cyl. There are guys out there that can tell you how to fine tune the reeds. Best Regards Capt,n