Holley help.

The fact that it was rebuilt a while should be forgotten. It sounds like something got in it and died in there. Very possible a warped boody and/or meterring block too. If the right side mixture screw goes in all the way, does it die? I would remove the left side mix screw, and using that long tube, shoot carb clean back into the passages. You should see bubbles/mist from the air bleeds on top, plus hear it coming out in the bowl, and throttle bore. I think whatever was in the needle and seat, is most likely all thru it now..The idle passages are the first to get comtaminated after the needle/seats. I'd go completely thru it again, and check stuff with a straight edge..