Early Quadrajet off idle stumble/hesitation

[Cgoldhill]

Recently professionally rebuilt 7042210 casting quadrajet that came stock on my 72 c10 350 4 speed.

When i first got it back, I put it on, set the idle mixture screws to highest vacuum reading and made sure my choke was opening all the way after it was warm. Truck drove awesome, nothing super fly but good low end torque.

Ive had the carb on for about a solid month and all of a sudden Ive gotten a crappy off idle hesitation that could sometimes turn into a pop through the intake if I blipped the throttle enough in neutral. While driving the issue translates into a initial bucking/hesitation as you go through the gears.

One day the truck was fine, the next it started happening.

Hei ignition, new plugs and newish wires, 12 degrees initial timing with vacuum advance hooked to manifold vacuum.

From what i see this early casting doesnt offer any kind of external APT (adjustable part throttle).

The issue is most pronounced anytime you blip or stab the throttle in neutral, whether its 1/2 or WOT.

Ive done a search and can only find info for later apt carbs. Others talking about rejetting but this is a stock 350, and the carb run just fine with current. Just need to rule anything out before i have to go be that guy asking for free stuff from my carb rebuilder.

Any ideas on what to check, clean, adjust?

This does not to seem to be any kind of a secondary air door gap opening issue.