I had the same problem with a 94 ZX7. Valve floated, then bent, then broke, then punched a hole in the piston. Bike had low miles and engine had never been messed with. I was doing some drag racing with it and was told that the engine design of the early ZX's caused oil starvation in the #2 cylinder on hard accelerations and during wheelies. You probably had a timing issue but this could be a contributing factor.