My 04 250f has ben smokin blue pretty bad, especially when first started after sitting awhile. The bike has also been getting harder and harder to start. Otherwise it runs real good with awesome power. I decided to open up the top end for a look...my first time but not the bike's cause I bought it used. To me, the piston and cylinder look decent and the ring gap is 0.013". The valve clearances were 0.004" and .010" (0.001" under spec). What concerns me is all the carbon buildup and traces of wet oil around the exhaust valve stems in the exhaust manifold. It is a real mess in there! Could it be that everything is ok except the valve seals which is causing the oil burning? Is there a minimum spec for the piston skirt? WHat is the best way to clean all the crud from the head and valves? Thanks!