also- for the gas leak
make sure that the 4 screws tha thold the bowl on are tight, and that the gasket is not deteriorated.
if the gasketis screwed up, you can buy a new one for a couple dollars from your local yamaha dealer.
Tell them you want the carb bowl gasket for the qt50.
if they dont have it for the qt50- tell them you want it for the pw50 (a little dirt bike that uses the same engine as the qt50-but is still manufactured today)
only do that if you need a new seal