improper intake valve adjustment or a valve sticking or burned!
A very unlikely coincidence that valve adjustment or a burnt valve would suddenly appear as soon as the OP swapped carburetors. It's not impossible, but unlikely.
What I do notice is once I first start the car, the Idle or RPM is way high. I always pump it once to start it now, if I dont it will start but die almost immediately. I have sat there and waited for the RPM's to come down but they just dont. Ive thumped on the throttle and that makes the RPM's come down a little each time I do if I space it out a bit. I dont know if the choke needs to be adjusted or just the idle.. Im not very knowledgeable with either of them frankly.
I'm somewhat confused because before you said the choke was definitely set properly, but now you're descriptions reveal that you don't really understand how the choke system works. It's fine that you don't know and that you admit you're not knowledgeable but want to learn, but I question from where you're getting all the information about the timing and carb adjustment. Is this particular shop doing all the work and telling you everything is fine? I ask because first and foremost, if you paid a shop to install and tune the carburetor, you shouldn't have to be worrying about figuring out this issue; you paid a shop to do that, and they should honor that agreement. If the car didn't have the issue before the shop worked on it, then it's their problem.
Now let's talk about the choke: When the engine is cold, in order to actuate the choke you must open the throttle (so you floor the pedal once). This action swings a cam onto the fast-idle step and also closes the choke butterfly most of the way to restrict air and enrich the mixture. When you turn the ignition switch to "run," electricity flows through the electric choke coil (a bimetal spring) in a function that will gradually open the choke butterfly as the choke coil heats up and expands. Note that an electrical coil has nothing to do with the engine (aside from some residual heat) but is a type of electric timer. Technically, if you turn the ignition to run but don't fire the engine, the choke butterfly will still open, which is why you should only turn the key to run as you go to fire the engine. The engine fires and idles on the fastest idle step of the cam in order to allow the engine to run in cold conditions. Once you hear the engine's rpm rising higher and higher, at some point you can lightly blip the throttle (don't mash it), which should swing the fast-idle cam onto a lower fast-idle step, thus lowering idle rpm. If you mash the throttle hard at any point after carb is on the highest fast-idle step, the cam will disengage and place the throttle shaft up against the hot-idle (normal idle) adjustment screw. Essentially, the engine is supposed to idle fast (at a set speed per your setup/carb specs), you should be able to decrease that speed gradually if you like by lightly blipping the throttle to get on smaller fast-idle cam steps, and then the entire fast-idle should go away as soon as you open the throttle wide enough.
Now, the choke butter is controlled by the electric choke coil, so even if you open the throttle enough to lock out the fast-idle, the choke might still be partially closed, which is normal depending on the engine temp. The purpose is so you can begin driving the car sooner when it's still not at running temp because the choke is functioning to lean out the mixture, yet you won't be experiencing fast-idle when idling down the road or at a stop. Are you following me?
to check the choke, with the engine cold, remove the air cleaner and open the throttle wide by hand. The choke butterfly should close for the most part. Go and fire the engine without touching the throttle. Check the choke butterfly. It should have about a 1/4" gap between it and the wall: too little=too rich, too much=too lean. The engine will stumble/stall in either case on a cold day. Once the engine rpm increases with warmth, give slight throttle by hand and let the throttle return to closed. Does the rpm decrease but not all the way down to normal running idle speed? Once you know the engine will idle at normal speed, give some more throttle by hand and see that the throttle shaft stop comes to rest on the normal idle adjuster screw (fast-idle is locked out). While you're doing all of this, allowing the engine to warm, watch the choke butterfly. How quickly is is opening compared to engine temperature? You can adjust the opening rate by turning the choke case, which will expand or contract the spring. You'll want to set the fast-idle speed per Edelbrock's instructions. Engines aren't designed to received full throttle blips when cold, so a poorly tuned choke could cause backfire issues when cold.
As for other things, where is initial timing set? Is this with or without vacuum advance hooked up? Is vacuum advance hooked to manifold or ported vacuum? It should be hooked to ported, no matter what other people might claim about the myth of manifold vacuum.
One more thing: how was the idle air-fuel mixture adjusted? Do you know how many turns out on each adjuster (this isn't the way to adjust, but it'll give us a ballpark idea? Let us know.
I was in a rush, and hungry when I said choke butter.
