I have a 09 yz450f it has a dr.d header pipe and fmf slip on. I've had the bike about 3 months. About a month ago I put white plastics and new graphics on it and I've noticed the rear fender on the exhaust side is turning brown... could it be jetted a little rich or? It runs great. I ride it every weekend at the track haven't had any problems with it since I've gotten it. Any insight would be much appreciated!