check the fuel pickup tube in the tank. Some gas is probably varnished over the plastic filter on the end of it. Mine did exacly the same thing when I first got it running. Go about 1 mile and then it would quit. After sitting a few minutes with the key in the on position, it would crank right up and go another mile. When I took the pickup tube/sending unit out, I couldn't even blow air through it. I used the end of a small screwdriver and an exacto knife to re-open the little slots.