My fa50 Suzuki 1985 had the same prob, i could rev it a lil but as soon as i revved it while on it, it would cut off. My neighbor suggested that all older motorcycles have same issue. Simply get your hammer and tap away. I tapped the carborater and the thing next to the carborater pretty good and it started up and ran faster than b4! It is suppose to loosen a needle that controls gas flow.