As far as the petcock, you can get rebuild parts here https://www.cheapcycleparts.com/oemparts/a/yam/500445daf8700209bc78f864/fuel-tank you should only need parts #4, 5, and 6, unless the petcock is badly corroded. If it was left with ethanol gas in the tank for some time, it will separate, and the ethanol will go to the bottom, where it can get into the petcock. If it is you would be better off just getting a new one. I have seen rebuild kits on eBay and I believe Rocky Mountain ATV. But they are aftermarket. The parts from CCP are oem Yamaha.


The above is my opinion. Your mileage may vary.
1994/2001 custom built XT225 with a ton of aftermarket parts.