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I have an 06 yfz 450 with 480 big bore kit and I believe the piston is 12:1. From what I have been told this is the most you want to go on premium pump gas. I rebuilt the motor 3 years ago and it has ran perfect ever since. The jetting was dialed in with the spark plug always brown. Only other mods are cam mod, exhaust, and k&n.

The girlfriend has been the only one riding this bike for about the last year or two. I rarely ever check the oil because I just change it frequently. This summer I went to go check it and it was almost a quart low ( Yes I know how to properly check the oil). I also noticed the air filter was cover in oil. I topped oil off and took it for a spin and the bike seemed to run perfectly with absolutely no smoke. Cleaned the filter and kept riding the bike rest of summer and fall topping off the oil after each ride as it was a couple hundred ml low each time. The air filter stayed dry rest of season. Bike has ran great with no noticeable smoke however our last ride a guy behind us mentioned he saw a little blue smoke only when the bike was decelerating going down hill. No smoke comes out when reving it. I figured it was valve seals or rings. I pulled the head off yesterday to find alot of white residue all over the valves and spark plug. One of the valves was all black. And the exhaust valves have a lot of white residue at the base of the stem. The piston and cyclinder look great. Valves were right in middle of specified tolerances. Oil looked clean not milky. No metal shavings magnetic drain plug.

Like I said bike has been running great and no smoke ( except on deceleration which I can not replicate when I take bike out to troubleshoot. Some guy had just claimed he had seen this so I don't know if he was seeing things or what). The bike is going through a lot of oil. Not losing any coolant.

The white residue makes me nervous. Is this sign of bad fuel? Running too lean? Something leaking?

Any help is greatly appreciated
 

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