I just bought a 2001 Yamaha Warrior and it has an issue with sudden stalls unless you catch it in time and rev it up a bit then seems ok for a while. This stalling happened only during a trip to southern tier in NY. I was at an elevation, but not quite sure how high. Possibly 1000 feet or less. Never has happened around my yard at sea level. Also while riding at any given speed or gear the motor hesitates if a consistent rpm is maintained. It is fine while increasing speed but hesitates if a given speed is held. I believe it to be all stock with exception to an HMF full exhaust. It is quite a fat pipe from the jug all the way thru. Could there be a jetting issue. I plan to take carb out and clean. What is the stock jet sizing for oe and what should the size be with such a free flowing exhaust such as this. I have replaced the fuel filter and live in western NY so mostly sea level, but eventually will be occasional trips to 1000-1500 feet. Thanks for any suggestions.