To some degree you are always going to have that issue you complain of , or, you're going to be too rich the rest of the time and risk dieseling, high idle, poor fuel mileage, and the associated conditions.Thanks. That sounds about it.
Reason: the carb is set and forget. It isn't dynamic with constant changes of richening and leaning out the fuel mixture based on measurements being taken like FI. To alter the mixture you need to adjust the screws.
When an engine is cold, some of the fuel being injected in the manifolds, passages, and such will condense onto the internal surfaces, effectively leaning out the A/F ratio. That's why it acts chugging, it's running lean, and, it's why giving a little gas pedal helps warm it up quicker with it running smoother while you do it for the 30 or 60 seconds. FI motors measure the A/F ratio, see its lean, and increase the amount of fuel injectors dump to raise the A/F mixture so you don't get that chugging/rough idle. Carbs don't do this. BUT, if you tune your carb to dump extra fuel so that it can have some condense when things get cold, its going to run rich the rest of the time.
GM experimented with some things to attempt to change this for carbs just before switching to FI in the form of their E.F.E. heater element baseplates between the carbs and intake manifolds in some motors, but, the metal grids the air/fuel mixture would pass though in those E.F.E. plates to be heated enough that ideally less fuel would condense prior to ignition on cold starts invariably melted over time. Seen plenty that were partially intact on disassembled motors.
So. If it works properly with good ignition patterns on the plugs and no issues when it is temperate out you need to make a choice:
1) leave it alone and deal with the normal warm up periods expected for carbed vehicles in cold weather
2) keep a notebook with set 'tune' adjustments for certain temperature ranges and keep adjusting your carb screws back and forth based on upcoming weather, a warm.amd a cold setting should suffice for Boston
3) set it to be rich when it's warm, but have less lean symptoms cold, and take the risks of damaging the cats with unburnt fuel, and all those other problems with potentially getting too rich mentioned above- dieseling, etc, etc. Maybe find a fine line where you sacrifice fuel economy and need to clean plugs and such more often, but, aren't quite as cold impacted. Sort of doesn't run quite as well or clean in warm weather, but, needs less warm up in the cold.