I have a 1996 big bear 350 4X4 that is in excellent condition. I bought it from a buddy a couple of months ago and he purchased it new and it still has over 50% of original rubber on it. I say all that to give you an idea of how it was taken care of and current condition. Here is my issue-bike runs great in every way other than when I will climb an incline then start the decent. At that time it will either cut out badly or die completely. This may also happen every now and again when coming out of a field into the side ditch. I have taken the carb off and cleaned with carb cleaner and compressed air, adjusted float per manufactures service manual, checked vent tubes, new, spark plug, and any other little thing i could think of. This isn't the biggest issue but is a pain when plummeting downhill head first with no power. Any help or advice would be appreciated.

 

ever consider your running low on fuel or the tank valve may be somewhat clogged?

 

Check the inlet manifold for leaks, Yamahas are rather prone to them and downhill with throttle closed is when the vacuum in the manifold is greatest.