Hey guys I have a 1987 Moto 4 200, I am getting a very loud noise when it is under a load, if you ease into the throttle it doesnt do it. Also it seems the longer you drive it the louder it gets. I dont think its the valve's, But it does sound like its coming from the top end. My brother said it sounded like Spark Knock, Can anyone help me out? Should i Just tear the top end down and make sure the valves arent hitting the pistion?