I need help with an engine problem

[Tommy]

Final Report (assuming nothing new pops up)

First, thanks again to all who took time to read and comment on my problem. I appreciate you all.

I ran the engine long enough to finish burning all the test oil from the exhaust and then rechecked cylinder 8. The spark plug looked fine and the compression was still above 200 PSI. So I took it for a 40 mile test ride averaging 2500 RPM or so. There were no unusual sounds, no unusual KNOCK ALERT warnings, and no smoke from the exhaust. So far as I can tell, everything is back as it should be.

The only substantial things I did to solve the problem were reset the lifter preload and install new spark plugs. My best guess is that some combination of old plugs, and insufficient valve opening on cylinder 8 caused that cylinder to not combust properly.

I added a dose of Sea Foam additive to the gas to help remove any carbon deposits on the valves and unstick the float valve if it is sometimes sticking. I'll be checking the spark plugs regularly to see if symptoms of the rich condition return. After the Sea Foam runs through, I'll also recheck the lifter preloads to see if carbon buildup on the valves contributed to the low preloads. If the preloads are still too low, I plan to get some slightly longer pushrods so the preloads can be set correctly.