I recently purchased a 1999 Yamaha 350 4X4 Big Bear. The problem I have is that the ATV has excessive valve noise which I thought would be corrected by a valve adjustment which it never had. The adjusment did next to nothing to eliminate the noise which seems to get worse as the engine heats up. There is no performance lost with the engine but I am concerned with the noise which is definately coming from the valves. Anyone familar with this problem. My local dealer told me the noise is common for my model and not to worry but would charge $200.00 to perform a full service which would include re-adjusting the valves.

 

Could the noise you hear be the cam chain? It can make a tickety tickety noise similar to valves, especially after warming up. Remove the cam cover from the side of the head and take a screw driver to move the cam chain (looking at the cam, chain to the left - back - where the tensioner is). If you have a lot of slop, or can move the chain a partial link up on the sprocket, your chain is probably stretched too far. Also roll the engine over and watch the chain - look for any "kinks" in the links as the chain comes off the sprocket. A bad chain will "kink" into a position whereas a good chain falls smoothly back into place.