it could be alot of things. how is your carbs. it could be a couple of things . here they are check your choke. make sure it is open, make sure your pilot jets are gunk up, check the fuel screw. the reason i say these things because i had the same issue. it was the fuel screw. see when your in neautral your not reving. so i think. so your ideling very low. try neutral while reving for like 2secs and see if it dies. it shouldn´t