So I was rebuilding the carb again with the Ford Kit this time. Much nicer than that generic one I had before. Worth the wait. This time I pulled off the spacer too and while undoing the coolant lines the vacuum line to the brake booster just snaps off the manifold elbow. It was as brittle as it could be right there, and it was full of carbon. So all new hoses for under the hood. Normally that's the first thing I replace, but these did not look that old. Turns out the vac line was probably original. I could tell from the cross section that it had been leaking for a while. So now I have a fighting chance at getting it to idle properly. That also explains why the spray test did not shoe any leak around the carb base. Still going to test the booster for leak. It definitely works, but that doesn't mean it doesn't leak.

 

Glad to hear you stumbled across the problem. Yep on the booster. Not only the booster itself but also check out the rubber grommet where the plastic vacuum check valve mounts in to the booster.

 

Yeah, that was worrying me as well. But a new booster would come with one. Hard to determine if the internal valve doesn't seal well or it's the grommet or a combination of both. We'll see what the vacuum test shows.