How much carbon buildup is considered normal. I just pulled apart the top end of my 2000 cr250 (I bought it back in January, so this is the first time I have pulled the top end on it) and there seems to be a lot of carbon. It also made the power valve very sticky. I went through it and cleaned everything, and the powervalve moves freely now. I put roughly 45 hours on this bike since I bought it, and the previous owner said he put less than 10 since a full rebuild.
Is this normal? Should I be rebulding this more often, or at least pulling it apart to clean these items?
I usually run 40:1 fuel/oil ratio.