Excellent advice from all. If nothing seems to help much, don't forget to check your muffler clamps. Most people don't use a torque wrench when they reinstall them after the new slip-ons are put on. If clamps are loose they can allow air to be sucked in when you back off the throttle. I know, it sounds kind of far fetched but loose muffler clamps can be the cause. Also, don't be surprized if your muffler clamps stretch after one or two uses and you have to buy new ones, expecially if you have been using the Armstrong method of tightening. About 40# if you use a torque wrench. Another thing to watch is how far up the muffler you locate the clamps. Too far up and it will take too much torgue to seal them. About 1 inch from the end of the muffler is about right to locate your clamps. Good luck.