Looks like this is a common problem. Mine just failed and was swallowed by the engine. This was at about 5200km on a '98 model. The first warning was the revs would not back right off at idle. About 1km later, after stopping, it would not kick start so I gave it a roll start. What a horrrible noise! Bits of alloy jumping around on top of the piston. Luckily I stopped it straight away and no piston or bore damage. Only damage was to my wallet. So, I recommend everybody keeps a close eye on the carby slide (throttle valve plate). Anybody know if Yamaha has redesigned the plate or somehow knows how to fix the problem?