[1 bad shee]

hey guys ive got a 96 shee it is still all stock....its running like shit started out back firing on the right side so i changed the plugs and still does it but not as bad,,,,a 300ex stock out ran me in a race today...it is stock also all but the pipe...but thats f*cked upso i ran a compression check 119 on both sides pulled out the reed cages they look alright....so can someone help me out with my problem? thanks