If it has a plastic gear anywhere, all bets are off. (I worked 1/2 a day on a 3.5 hp. only to finally find the valve timing was 1/2 a revolution off.)
When setting the timing, keep in mind that at TDC between the compression and power strokes, Both valves should be closed. Both cam lobes should be oriented opposite the top of the cylinder. When I say'opposite' I mean one lobe 45 degrees to one side, the other 45 degrees to the other side of a line parallel with the center of the cylinder.