The only thing that i can think of is do you have the Flywheel collet on the crank. If not the flywheel will not be able to turn over the engine at all. And that would leave you with eratic engine behavior. If the engine even would start and stay running. Another thing is do you have the clutch nut on tight. This has happened to be a couple of times that the nut will loosen it's self from the vibration of the motor and such. When the clutch nut is not tight it will not apply enough pressure on the flywheel which will in return not have enough pressure to turn over the engine. If the flywheel is not turning over it will leave you with eratic engine behavior. These are the only things that i could think of that might leave you with those types of engine problems. Ihope this helps you with the problem