I have a dr650 with a bad knock. Pulled my head, rings look ok, cylinder walls are ok, the right side of the piston at the top is really black, maybe from blow-by. But the valves look terrible. The intake valves are black and the exhaust valves are crazy white. Would this be from the engine running way too lean or from the blow-by? The valves were cleaned and lapped 1500 miles ago, so this all is very recent. I am burning through a lot of oil, 1 liter every 500 miles, but I can't get new rings in Chile, and I'm 250 miles from Ushuaia. Doesn't really explain the knocking. Unless it's a detonation issue. Any suggestions?