I just recently went through my brothers Quadmaster 500 after it had set idle for years. Had to replace carburetor and fuel valve. Everything was a sticky mess with part of the plastic looking like it was melted. Soaked fuel tank for a week and still had varnish coat inside, ended up using a whole can of carburetor cleaner to get it cleaned. Using Gumout tune up in fuel, hopefully it will take care of anything that I missed.