Small Engines (Lawn Mowers, etc.): Briggs 16hp opposing twinn, cylinder machines, valve clearance

Question
I have a 16 hp opposing twin that I installed on a gokart, it does run, but not well enough to pull its own weight. I have cleaned and adjusted carb, as well as replace the carb with another one that I had from another 16hp opposing twin. Have changed coil, spark plugs and have great spark. However when running it splatters gas out of top of carb, no matter what I try it still does this. I have checked compression but not sure what it is supposed to be, have 40lbs in one cylinder and 60lbs in the other. what about valves? help would be appreciated. thanks Michael

Answer
It seems that one of the valves is not seating properly in the cylinder with the lower pressure. My experience with this symptom has been with single cylinder machines and it usually meant taking the offending valve out for a cleanup, a cleanup of the valve seat and port area, reseating and valve clearance setting. Best done by professionals unless you have the gear and experience. Terry