sticky valves

[gwmac]

3.0 with JE pistons and webcams
Fresh heads with new valves and guides, started engine with Aviation fuel
because I only had ethanol available, ran well for about 10 minutes then
started randomly huffing out both intake and exhaust on random cylinders.
Quits if I put enough Marvel Mystery Oil in for it to smoke.
Replaced av gas with the highest octane ethanol i could find and added
.5 oz per gallon Marvel MO and valves are still randomly sticking.
Looking for ideas before pulling engine back out.
HI HO.

[john walker's workshop]

Does it get clacky rocker noise when it happens?

[gwmac]

No I havent noticed that but it is open headers.

[dannobee]

Try the "AC Delco Top Engine Cleaner." PN 10-3015

[E Sully]

First thing I would do is pull the spark plugs and see what shape they are in, and if you have a bore scope and have a look inside. Then maybe a compression or leak down test to see where the problem is. I also wonder if the open headers affected the fuel air mixture.
You might have used too much Marvel Mystery Oil. This is from an FAA inspection of a Lycoming aircraft engine that failed.
"The operator told the FAA inspector that the red color was from an additive placed in the fuel tank, at a rate of one quart for each refueling. Examination of the engine revealed low compression on all cylinders, ranging from 44/80 to 5/80. Air bypass was noted on all exhaust valves, and on two of the intake valves. The number two cylinder was removed, and evidence consistent with detonation was found on the surface of the piston, and on the valves.
According to the FAA inspector, the additive that was added to the fuel was Marvel Mystery Oil. An empty 1 gallon can of Marvel Mystery Oil was found in the operator's trash. Instructions found on the can stated that the correct ratio for mixing with fuel was 1 part additive to 100 parts fuel. The contents of Marvel Mystery Oil were 74 percent mineral oil, 25 percent stoddard solvent, and 1 percent lard."