frenchie, Is the engine sounding rich at the viabration level? Also you might try the prop in a different position. Maybe check the balance of prop when you have it off engine. Even try a different prop may help. If you have the flywheel that was on that engine..check its balance. Maybe it had more weight in a certain spot to balance engine!!! I have seen bolt on bob weights that said right on them...make sure to reinstall in same position. Good Luck Capt,n