verslagen1 wrote on 07/13/15 at 14:54:53:Digger, as Dave and I concur, it's most likely a valve adjusted too tight and not sealing. The valve has to sit on the seat long enough to cool. The carbon looks just like the carbon that accumulates on top of the piston.
If you could, get an eyeball on a stick and look at the top of the piston to rule out oil from below (worn rings) vs. from above (worn guide).
if it's not oil, then it's gas additives. ARCO used to be famous for the sulfur content and build up on sparky.
Hi Ver,
Just an update on the intake valve clearances:
Both intake valves showed 0.003" of cleanrance, which is what I set them at almost 4000 miles ago. (FYI, the book says the range of allowable clearances for the intake valves is 0.003 - 0.005 in).
Took a quick peek at the top of the piston, as seen through the spark plug hole. Looked the same color as the spark plug insulator did - kind of a mid-level gray color. No black carbon-y stuff in sight.
Will take another peek at the top of the piston after the head cover is removed and I can get a better angle...