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From Another C3 Forum:

"I recently purchased a '73 base motor 4 spd with 93k miles. Edelbrock 600 cfm carb and dual plane intake, HEI distributor, new NGK plugs, and long tube headers installed about 200 miles ago. At around 2000 rpm it had a slight miss so I replaced plugs because 6 out of 8 had oil on them. Put 80 miles on it, runs good and no smoke. Before plug change it had some black smoke and soot just on warm up. Checked PCV system and it has good draw to it and it doesn't appear to have excessive blow-by. Is oil on plugs going to show up again or just an anomaly? Thoughts"?

I have been twisting wrenches for over 50 years and I don't know what a "slight" miss is. Is it a miss or a "kinda sorta" miss or "I think it's a miss"? On a cold start the choke will make the air/fuel mixture richer until the engine warms up enough to fire a leaner mixture and during the warm up the rich mixture will put some soot on the spark plugs. After warm up the increased combustion temperatures will burn the soot off.

However oil on the plugs indicates leaking valve stem seals or worn oil rings. With only 93,000 miles on it I would suspect the valve stem seals as being the likely cause of oil on the plugs because after a hot shut down some oil will drain down the sides of the valve stems and onto the valve's heads. If new valve stem seals don't solve the problem then new rings are in order.
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