Your problem has 6 letters- - - - -"H O L L E Y". Buy another Q jet, with the correct part number for your engine. There are several hundred variations of Quadrajet carbs, and Holley sells a few "One size fits nothing" replacements. You could try loosening the screws that hold the primary throttle plates to the shaft and letting them close fully with the idle speed screw backed all the way out, then retighten the screws. The throttle plates are possibly misaligned and dragging on the casting a little, or more likely, the casting is a little out of round.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!