I take the vacuum line off the brake booster and it smooths right out.
A vacuum leak leans out the mixture the same as pulling the choke out a little fattens it.
My inner Spock tells me you have a rich mixture at idle.
Float level too high?
Should be square with the carb top hanging upside down or equivalent check.
That has to be 100% squared away - involuntary pun - before anything else.
Moving to the 1st circuit, the idle.
The needles need to be in good shape, look at them.
If they're worn out, replace them.
They could probably be cleaned up if replacements couldn't be found.
Seat the needles in fully several times, but gently, preferably by hand and not with a screwdriver but if with a screwdriver do not force the needle seat shut excessively hard.
Turn the needles back out a couple turns, start car and adjust for decent idle, but more importantly re-adjust when hot.
This adjustment has to be made, again and as final adjustment
hot so that the choke is fully open and engine up to to operating temp.
Anytime on the car, with engine off, you can pull both needles - if you're not familiar with the carb, run the needles in gently till they seat and record the exact number of turns - do not mix them, blow the seats out with air and reseat is you suspect crud could be interfering. It can happen, especially with the float needle/seat.*
Probably not so much with a newly rebuilt carb, if you did the work yourself. If it's a reman, it's probably full of beadblasting sand, or there could be a dead mouse holding the float up. Extreme sarcasm emoji.
I usually run the right side in til it - go slow - until it just starts to get too lean - sounds like crap, faltering - bring it back out to a nice smooth point, and maybe just a teensy bit further for a better idle with engine cold, and power.
Lean = backfiring through carb with cold engine and does not make good power or keep engine cool. The latent heat of fuel cools the engine as it goes through so it's got to be right.
Besides the idle circuit, remove the float and make sure the jets are seated correctly, with proper fitting screwdriver.
This is all assuming your choke is opening all way.
*If you suddenly have crud in the carb needle seat flooding the carb out, rap or tap the side of the carburetor with a wooden hammer handle - non marring - it works wonders, it will dislodge the particle and the float level will normalize.
In these parts, the PNW, everybody always deemed Mopars to be "cold blooded", that' what I heard growing up.
Translation, you don't know how to properly set a choke to work as intended, but in many cases the heat crossover in the manifold is plugged with carbon, for better or worse. I'd have to say the Dodges were just climate ready as it has warmed up a lot, we may not need heat crossovers much longer, and I loathe the idea for pure performance.
