Please help me diagnose this 273

SeattleQQ1Fish said

The needle was bouncing around during the vacuum test. Not severely, but it wasn’t perfectly steady. I’m not sure what power valve is in the carb, it’s whatever Holley put in it new from the factory. The way I checked for a leak was to spray carb cleaner all around the intake and base of the carb looking for a change in rpm.

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With a stock or even moderate cam, the vacuum should be steady, not bouncing.

BTW, sticking intake valves would make this occur. Any clue on if this ran OK before the PO made the manifold and carb swap? Or how long it might have set? Running old fuel through an engine can create very bad deposits on the intake valve stems that can cause them to stick and even jam open. (BTDT). Have you pulled the fuel tank and drained it, checked for rust and so forth? Bad old fuel will mess you up every time, and the new ethanol goes bad (oxidize) very quickly, plus pulls in water and forms a gum if the fuel sets and the ethanol separates out.