Sounds like you have a place to begin. I've worked through several issues with no-start or poor idle problems with my Q-jets. One time while re-connecting the hard vacuum line from the brake booster to the rear of the throttle plate I heard an unusual "snap" sound. I couldn't find any immediate reason for it, so I continued. It took forever to adjust the idle mixture and timing to get it to run, but even then it ran like a real dog. Idle quality was terrible, and it seemed to be running very rich. I decided to remove the carb to take a better look at it. When I did, I discovered that "snap" was the sound of the throttle plate cracking from my having over-tightened the brake booster line. Swapping the throttle plate solved the problem.
This may not be what happened to your carb, but you have what I call an erratic problem - one that doesn't seem to make any sense based on the operation that was just performed on the vehicle. Often it takes a complete reversal of the procedure to inspect every part. Don't be hesitant to remove the carb for inspection, as well as any other vacuum related parts that might not necessarily be suspect under ordinary circumstances. Good luck !
