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I think you have at least two things going on here. Your main jet on the primary side may be a little too lean. Works ok in warm weather but shows signs of leaness with the colder weather, but we'll get to that later. I also think you are showing signs of carb icing after driving at a steady speed in cool temps with hesitation and stalling upon stopping--the motor can be fully warmed up and this can still occur. It is essential in moderate and cold climates to have a water heated manifold for the Weber to work properly. Having a closed air filter housing with regulated preheated air from around the exhaust manifold should be incorporated too. At least one of the two systems need to be used. Does you manifold have a coolant tube built in? If it does you need to hook it up so coolant flows through it. If it doesn't, here is a tip--Renault LeCars use a similiar Weber, though with smaller throttles and venturis, the outside dimensions are the same. They use a cast aluminum spacer with a built in water pipe to mount the carb to the manifold. You'll need half inch longer studs for your manifold and two mounting gaskets. If you can, you should devise a filter housing so you can utilize preheated air--Vegas and Pintos used a Holley version of the 32/36 DGAV. Even with the RAM type foam filter and chrome grillwork you can devise a cover from heavy gage foil to capture warm exhaust manifold air. The hot air thermostat/valve in Volvos works very well. You can move on to dialing in your carb once the basics are in order. Does the accelerator pump nozzle give a good stream--and respond to small throttle inputs? All manifold bolts tight? float level correct? etc. Unless you have diagnostic equipment to measure your exhaust as you drive you'll need to rely on the seat of your pants -- and a calculator for MPG monitoring. It's very difficult to feel when you've got it right if you move from lean to rich. It will seem to run better and better with each change until you come to realize you've gone way too far. From what you said about your running condition I think you will need to go a few steps richer right off the bat. If your main jet (primary side) is in the 120-125 range a move to 140-145 is in order. I suspect the change will be substantial. The engine should feel much stronger and responsive. Go leaner one step at a time until you experience lean running--hesitation/holding back on acceleration-feeling like you always need to step just a little harder while cruising at a steady speed-stalling upon stopping. At that point go back to the last main jet used. You can play around with idle jets once you have the main jet settled. Air correction jets may have to be changed as well but along with the emulsion tubes they are in the realm of very fine tuning. One more thing relative to your particular car--is your distributor vacuum set up correctly? Some distributors use manifold vacuum, others ported vacuum. One other note for those with electric choke Webers -- I always found them to come off choke too soon in my NY winters. An ignition resistor for an old Chrysler car wired in-line slows them down and probably helps preserve the choke heater element.
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