Lon. you are welcome to give me a call ,, 314 609 6568,,, engine might be sucking air from somewhere , but for the life of me I cant think of anything,, I remember the odd carburetor, but it worked pretty well a few years ago , I remember the rotary valve was the last one wayne had and it fit very well , maybe try to see if there any loose screws on the round crankcase cover or maybe the cylinder bolts could use tightening , worse case , send the engine to me and Ill fix it no charge m, I have a " mule bike " I can test run it in to make shure it's ok, sorry you're having trouble , mat even have something to do with the throttle control . all the best , Larry.