I had an 05yzf450 and it started burning oil not long after it had a new piston rings, head, timing chain etc. Would race one day and check oil, had to add a lot. SOLD IT! Now my 06 with minimal hours is burning oil. Definately smoke on start up. Would that be the rings or the valves and seals. Was thinking more the rings. If it was the seals, wouldn't there be oil in the exhaust head pipe, or would it just burn off to fast to notice if i took the head pipe off. Plus, i had the motor apart recently due to a kinked timing chain that was skipping cam gears so i pulled the motor down to the piston just to check things out. Head and valves looked good IMO. I did a top end and checked valves on a buddies bike last weekend and found that one of the exhaust valves wasn't closing all the way due to carbon build up. We just cleaned the head and valves/seats and put new seal on that valve. New pison/ring/timing chain. Runs great. His was burning lots of oil too. What is an average amount of oil to be losing on lets say, a race day. 15 minute practice, 2 15-20 minute moto's.