Goose is right on this. The problem is usually caused by an exhaust leak or carb problems. in my case it was several pin hole leaks in the "y" pipes. The "y" pipes are made out of a milder steel then the front pipes, why, I don't know, but they will rust and get thin over time. You need to take good care of these pipes because they cost something in the neighborhood of $450.00 each. If not the pipes then maybe your carbs need some adjustments. plugging the AIS is a waste of time.