Buick quadrajet idle air screws

[Tdwohio]

Hi, I have a Buick quad that Cliff rebuilt for me. I sat in the box a while before I had the car ready to be started. The engine starts and idles pretty smooth. My problem is when I put the car in gear, it dies. I corrected the low idle, and this helped, but still have the issue. After running for several minutes, it will keep running when put in gear, but stumbles coming off idle. When cold, it stumbles and chugs like it's only running on 3-4 cylinders when attempting to drive it. Letting off the throttle, it drops back to idle unless it dies. It will restart and idle. I have adjusted the choke, ( electric conversion) and it seems to pull off correctly. I attempted to adjust the idle jet screws, but turning them either direction as much as 1 full turn has no impact. It doesn't increase or decrease in rpm or idle roughness. I had it at a local shop that rebuilt my tranny, and during the test drive, he felt there was something wrong in the idle circuit.
Any suggestions on what I need to do?

[Rhett]

understanding most carb problems wind up being ignition, check your mechanical advance weight return. Replace the springs in the distributor with the heaviest ones you can get your hands on, and see if it still does it. I'm willing to be you see quite a difference.

[Shiny]

This^^

Start by getting your timing where it belongs.  Cliff has some great online guidance on how to figure out what timing your engine wants and how to get it done.  Not necessarily simple, but a little investment here will go a long way... plus you will KNOW what your timing curve looks like, even if you decide or need to modify it later.

Dive into your distributor or send it out to get it set up.

[Cliff Ruggles]

A carburetor part number would help.  Been quite a while since I've done any builds so probably woln't remmember it. 

I'd also be interested in the engine specs, and where the initial timing is being set at.  Stalling when placed in gear is just as often a distributor issue as it's common for folks to install spring/weight kits to get the timing in sooner leaving some of it in at idle speed and it drops out when the trans is placed in gear slowing or stalling the engine.

Anyhow, more info is better than less.....