Fuel percolation on shut down and running down into the ports and drying on the hot valves, leaving a build up over time.  The exhaust valves would not be subject to this.  Just a possibility.  Joe-JDC

JDC

It would be interesting to use a boroscope to check the combustion chambers and ring packs for carbon buildup.

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OK, thanks Ted and others.
The cam was installed out of the box. I will be installing a roller chain with multiple keyways so I will be able to degree the cam correctly, I haven't checked where it's at now yet but plan on it. The heads and cam only have 10,500 miles on them. Has Teflon seals. The guides are spiral type, could that be a problem? Valves were new. The bottom end has about 20K on it. I will be pulling pistons for inspection and new rings. Combustion chambers and piston tops look normal.
I opened this can o' worms because the compression test readings had dropped off especially on one cylinder. Valves were seating fine, must be the rings/pistons at fault there. I'll post what I find.

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