My sportsman 800 was running fine for 2 hrs. Without warning it sputters and stalls. After I let it set for a short time I restarted and was able to ride down the trail for a mile or so before it did it again. When the key is turned on I can hear the pump but it will not start. Fan works, rad. is clean, heat tape is in fair condition on the fuel tank. After I let the machine cool down it starts and runs fine until it gets hot again. Any thoughts on what I person can ck.?