I agree with Tom's read on this. I suspect your problem originated in the petcock. An old tired carburetor with wore pins and seats that don't seal as well as they did when they were new all contributed, but not the cause. Petcocks can be rebuilt. One problem I see with the stock fuel delivery process on these bikes is the vacuum part of the equation. Anyone old enough to remember vacuum operated windshield wipers would agree that if there is a better way, lets go for it. As Tom mentioned, the Yamaha Raptor petcock is a plug and play replacement, allowing gravity to feed the carburetor rather than the vacuum system pumping the fuel to the carburetor. The only real down side to this is that you will need to manually turn the petcock on and off. If you don't turn it off when you shut down the bike, you could very well be dealing with an engine full of fuel again. And if you miss the signs of a hydrolocked bike
, you may be dealing next with a bent connecting rod.
Your call. If you want to rebuild the petcock, we can steer you onto rebuild kits. If you want to modify your current petcock to gravity feed, this is possible, too. If you want to convert to gravity feed only, with the reliability a new petcock and components brings to the table, we can provide you with an affordable solution.
Your float system on your carburetor "shouldn't" allow this. With age and wear, dirt, varnish buildup and bad luck, things hang up and it happens. The best solution to avoiding this in the future is to shut your petcock off every time you shut off your engine.
In the "old days", where ever you saw a bunch of bikes parked, it would be a safe bet that at least one had a bad petcock and was developing hydrolock as you watched.