My customer who purchased the engine had the same problem. Ran in one race day no problems. raced yesterday, ran 5 laps engine died. brought it to pits, it fired up and ran great. went out again, engine died after 5 laps. Then we couldn't get the engine to fire at all. Changed the carb, same thing. Then tried a new carb, nothing. Driving home my buddy called me and said gotta be in the valve cover. Im going to check this week.