If the bouncing Vacuum gauge quit with the vacuum line pinched, and the line plumbed to ported vacuum, then, your throttle is too far open, because at idle, that port should be dead.
But if the line was plumbed to the intake-port, then the possibility exists that the diaphragm is fubarred; you would have to watch the timing light to see if it is similarly bouncing. if it is not, and nothing changes at the timing marks when you pinch the line, then I'd go with a bad diaphragm.
If the carb floatbowl has already been proven clean and uncontaminated;
Then I would just remove and clean the block under the choke plate which carries the emulsion tubes and air-bleeds, and make sure the gaskets are correct, and make sure the Accelerator check-system is complete. Going from memory, Some have a pointy check brass valve like a float valve and others have a ball with a weight above it.