I drive a 1998 Polaris indy 500. every now and then. almost ecery time i go and ride i will be going around 40-50 and then out of nowhere it will like start to loose the RPMs and it will go like 0-5 MPH and i have the throttle pinned down. also when this happens it usualy fouls a plug. if anyone has had this problem can you tell me how i can fix this so i can go riding more. thank you