Trying to run down a vacuum leak on a car right now. It's got an early 80s 305 with a Performer RPM intake and a Quadrajet.

The intake is a square bore and uses a Mr. Gasket adapter to adapt to spread bore. The only vacuum accessories attached to the carb are the brake booster and a vacuum advance. The motor does not use PCV currently (aftermarket valve covers), though I think it could be hooked up instead of the breather that's on there now.

The motor is mostly stock with a mild cam. Nothing radical, and in a previous car it was mostly smooth idling. The carburetor also is healthy and was used as recently as last week without issue on another SBC.

We've already replaced the carb base gasket as well as the gasket that goes between the adapter and the intake. We've also blocked off the brake booster line manually once and then measured vacuum to ensure the booster wasn't leaking. Also, all of the unused vacuum lines (including for the PCV) on the carb itself have been blocked off.

All of that and still only about to pull 7-10 Hg/in at ~800 RPMs. If you idle it up to maybe 1200 RPMs or so, the vacuum jumps to 15 Hg/in but the needle is erratic. The car only runs well if you manually choke it pretty sharply, otherwise it's too lean.



Any ideas on what else to check?