It's always bugged me when I service the air filter that it's generally clean everywhere except for the area right under the intake hole. Because the filter presses up against this opening, it gets clogged quick and has to hurt airflow. I first tried a large washer on a 1" spacer to hold the filter back but it wasn't enough so I bent some stainless strap and made a standoff that spans the whole opening. I left the dirty filter in and have put ~300 miles on since. You can tell that air is flowing down to the rest of the filter now and the difference when free-revving the motor is obvious. .