I've looked around and have seen a few different air filter things for this bike, anywhere from just changing to a K&N filter to filter pods to a box mod on a 3rd gen. I was wondering if anybody has done something to their bike for a noticeable improvement no matter how small or large. Airbox, no air box, air box mods? I know that it also may require some rejetting or carb adjustment. Please let me know your thoughts, and what has worked for you. Thanks!