Small Engines (Lawn Mowers, etc.): Engine runs rich, honda gx160 engine, genuine honda

Question
Hello. My kids have a new go-kart with a chinese copy of a Honda GX160 engine. Unfortunately this only runs for about 15-20 minutes before fouling the plug. This is just over richness not oil fouling. I also have a genuine Honda engine on a water pump. I have swapped the carby and air filter from this engine to the go-kart, checked the valves, checked the ignition, tried a hotter plug, made sure is wasnt over full of oil and done everything I can think of and yet it still fouls the plug. When running it goes well with good power and no hesitation, but eventually runs rough as you would expect with a fouled plug. Any ideas on what else I can try? Thank you.

Answer
John
The Chinese versions of the Honda engines have problems with the valves especially the intake valves. What happens is that the valves are not opening completely because of the cam being out of round. There is nothing that can be done with it except rebuild the bottom end you may want to lean it out a little it may not have the power at first but when it warms up it should smooth out.