Hello, wondering if anyone could assist with my problem. I have a 20 Horse onan in an John Deere tractor. I installed new pistons, rings, camshaft and crank bearings, and valves along with the head gaskets and main gaskets. This machine ran good with intermittent use with total of about 3 hours on it. It started missing. Finding it only runs on one cylinder. I rechecked compression on the non firing cylinder- 115PSI. replaced coil, points, plugs and wires as spark seemed weak. It has good spark and good compression but cylinder will not fire.. Any assistance would be greatly appreciated.