Hey looking at 2001 Yamaha Warrior 350. Just wondering if the top end needs to be rebuilt or how often do they need to be rebuilt or how do you know if it needs to be rebuilt. And does an upgraded exhaust and a jet kit put more stress on the so that it wears out faster.

Thanks in advance

 

Is it smoking? has it lost power? a quick compression check will tell you if the valves and rings are sealing, what problems are you seeing that makes you wonder if it needs a rebuild? more info would help.