There is an EGR pump under the front fairing of the bike, right by the horn. It recirculates oil, and unburned fuel that seeps past the valves, feeding it into the airbox. That is why some folks complain about the filter being soaked in oil. I had bypassed it, and capped off the tube, but then worried about the oil getting trapped and eventually seizing the valve, so I put it back together. If you did change the airbox, you would need to either hook this system into the new filter, or cap it off.