74 Dart Swinger Carb issue

i'd try rebuilding it again and double checking the critical tolerances. it's possible you got a crap rebuild kit and something in there went sideways.

just out of curiosity, how's the fuel system? filter, lines, etc? some of that might be on it's way out or compromised and leading to detrimental effects at the carb.

failing all that, you could source a used piece and roll the dice. or there's the hong kong phooey carter 2bbl knock offs on amazon. i've had good luck with those thus far.