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I have been trying to finish up my wife's 69 fastback and I have found a problem. The engine did not seem to be running quite right. Not a new engine. But the one that was in the car. I checked the cylinders and found 3 an 7 were not firing. I checked the plugs and found #7 was in need of replacement. After a new set of plugs and wires I still had nothing on # 3. I did a compression check and had between 145 and 160 psi on all except #3, with only 30 psi. I am going to pull the valve cover to see if the rockers and valves are moving. The car was stored with an open intake manifold for 8 years before I rescued it. Does anyone have any other suggestions?
 

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You are going about it correctly. Could be a valve stuck open. Turn it over and watch the valves on #3.
 

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Try a little Marvel Mystery Oil down the #3 plug hole and see if your compression improves; could be stuck rings, and if so then the Marvel Mystery Oil will loosen them up.
 

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When you pull the valve cover be sure you how hard it is to push the valves down. I had an engine that had a 2 spring valve spring and the inner one broke. You could not tell from a visual inspection. It just didn't seal the valve well. Anyhow i didn't check the spring pressure before i pulled the head. Live and learn.

Another test you can try is to bring the bad cylinder up to the top of its stroke which you can tell from having the spark plug out. Once it is at the top by definition both valves should be closed. They make air fittings that will work on a spark plug hole to hold a valve up when you need to change valve springs without pulling the head. Start pumping air into the cylinder and try to find where it is coming out. Carburetor, tail pipe or engine block, cooling system., its got to go somewhere.
 
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