Also, double check your valve clearance like bgi said above. Mine was off straight out of the box. In fact, I had to reset the valve clearances on all of my four strokes after the initial bench runs. If you can slip the supplied 0.1" gauge in between the rocker arm and the valve stem, then your valve clearance is too loose. Get either a 0.01" or a 0.04" feeler gauge and use it to set the valve clearance. Is your prop balance?