That's right folks, if you are having any symptoms of a failed petcock, replace it. Replace it now! Don't botch it. Don't install some inline fuel valve. Just replace the darn thing. It's $68 from Yamaha and comes with all new tubes and everything. Its fancy.
But that $68 will save you from this:
Also, install 4 new needle valves in your carbs while you're at it!