Carter 2BBL carb- I am stuck

There's lots of good info here. I'd like to add a few notes:

To start out with, as another member mentioned already, there is some confusion about how to adjust mixture screws. There is no preset number of turns out or in. When you see that mentioned, that is in reference to a baseline to get the engine to start and run.

Usually that's about 2 turns out from lightly seated. However, you adjust the mixture screws as already noted- start with one side and go clockwise until the rpm slows, then back counter-clockwise until the rpm slows again. Somewhere in the middle of that range is the sweet spot where the engine idles the fastest. That would also mirror readings you would receive from using a vacuum gauge. Someone said just "gauge". They meant vacuum gauge.

Ok, so if your engine does not respond to adjusting those screws, it could be the all-encompassing vacuum leak which is allegedly responsible for 98% of all engine performance issues.

However, you ruled that out. So, we have to look at other reasons. When I get a carb that will not respond to mixture adjustments, the first thing I do is check the....wait for it...ignition timing. Why? Well, base timing that is adjusted too far retarded or advanced can artificially decrease or increase the idle speed, respectfully.

So, if you have timing that is too far retarded, then the idle screw of the carb has to be run in so far to make it idle that it's actually off the idle circuit and into the main circuit. Then, no amount off adjusting those screws makes a difference.

Conversely, if the timing is too far advanced, the engine speed will not decrease enough with the idle screw. It'll still run at 1,000 rpm with the idle screw taken out and in your hand. A lot of people miss this and blame the carb, so check the timing with a light, vacuum advance line removed and plugged.

If that checks out, then there may be an issue with the carb. Historically, those BBD's tend to NOT idle at all. The pickup tubes are very small and get plugged with debris and the idle circuit quits. Then, again, the idle screw has to be ran way in to get it to idle and it's once again into the main circuit and no response from the idle screws.

You can check and clean those. Pull off the top of the carb and look for the two screws in the center that hold the venturi cluster on. I think it's only 2, all of my carbs are still together. Take those out, pull the cluster out and inspect the bottom of those tubes and see whether they are clogged up.

As far as the drainback issue goes, all of mine have done it but your case seems severe. You may want to pull the carb, fill the float bowl with gas and sit it in the sun to recreate the same conditions as under the hood. If it evaporates or you see gas under it, you have a clue then.

The only other thing I can think of is that one of the check valves in the fuel pump is bad and letting the fuel flow back into the line.

Have you checked the rubber line back at the gas tank? Those can get cracks in them and suck air, which causes the fuel line to lose it's prime and if it gets bad enough the fuel pump finally is unable to draw enough fuel volume to reach the carb. I would inspect that carefully.