Asked about this engine a couple times but this is a new problem. The engine had to be at full throttle to start and we found a weak spark. Replace the voltage rectifier and the power pack. After everything was put back together, engine started better but started to backfire. Traced it to cylinder #1. Swaped plugs, wires and coils, still did the same thing. Ran fine with only 3 cylinders and when I connected #1 it would backfire. Got to looking at the top of the piston #1 through the spark plug hole and it looks dry. Other 3 look wet. Took off the carbs and cleaned/inspected them, still the same problem. Any advice?