The vacuum lines that go to the air cleaner - you said they weren't connected. At least plug them, there's your vacuum leak. I think they operate the damper that mixes hot & cold air coming into the air cleaner.
I think(??) the carb is mostly normal compared to old-school carbs. But I didn't really work on dad's car that much. Besides, his was '77 and maybe wasn't exactly the same as yours.
The 3rd barrel is supposed to run richer than the primary. In that stratified-charge CVCC engine, the rich mixture from the 3rd barrel ends up near the spark plug, so it can ignite. The rest of the charge can be leaner, because it doesn't have to be ignited directly by the spark.