This moped runs good, but after taking the carb off and cleaning the gunk out of it, when started, it wants to rev up real high for a while then comes down very slowly and eventually will die. Try to re-start and it takes a little while(a few tries) and will start again. When given throttle, it revs up high again and comes down slowly....will run good for a while and eventually want to die. Please help. P.S. I can ride it up and down the street all day long, but when idling, this happens.