We have run a couple of GX340's that we got used,did'nt know how many hours on them,ran them for two season,stock form, advanced the ignition timing(makes them rev noticably higher, we think about 6000 rpm) and no trouble. We even ran one of them in the auto-cross,and goofed around with them a lot at home,pounding the tractors a lot to see what would break,so we could fix them,and not have that happen in a race.No trouble with the engines untill now, one has a noise in it looks like exsessive end play on the crank. so we will fix that before it blows and do some real work inside with the cam and compression as well as getting rid of the balance shaft(rotating weight)and lightening the flywheel. I know a guy that raced go-karts and was in an open class, he used a 9 hp honda,he said it dynoed at 22 hp he took 4lbs off the flywheel used all stock honda parts, and ran 6800rpm all season with no trouble. So go ahead wind it up.