SOLVED! 318 2500-3000 rpm idling issue. Don't think its a regular vacuum leak. Swapped 2 intakes, 2 carbs ,and 6 different gaskets still no luck.

cookietruck said

Wild about the head gasket rivet, I would be frustrated trying to find that one I know.

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It wouldn’t idle below 1800 and 5 out of 8 cylinders were making heat. It took me a while to find it, and I didn’t find it until I yanked the engine out and disassembled it. Like I said a leak down test woulda found it.