I have a 04 yz 450. I change the oil about every 2 rides, when I change the oil, the oil is burnt. MY riding buddies say they can smell burnt oil when they are behind me, however my bike does not smoke. I suspected my clutch plates, so I replaced the friction plates,steel plates and springs. I rode last weekend and after one ride my oil is burnt again. I have been using bel-ray 20-50 semi synthetic, and I change my oil filter every 3 rides. Any info would be greatly appreciated.