Yeah, petcock tends to stick and leak petrol into carbs on these bikes. Along with leaking float-valves and you've got hydrolock situation. I got 2nd 1985 parts bike that had "seized" engine for dirt-cheap. Turned out entire crankcase was filled with petrol, hence "seized" engine that won't crank and locks up rear-tyre when trying to bump-start.
I ended up rebuilding petcock & carbs on that bike and gave it to my brother!