Dan, thanks for the tip on the electric choke upgrade. (But I still don't think the choke assist is involved in this specific problem unless it's somehow heating when it shouldn't.)
You may well be right, but the point is that the stock choke system tends to give cold-blooded behaviour like this what you describe, and they cannot be adjusted. The electric choke kit replaces that primitive system with fully electric modulation. That works better, and plus the adjustability means you can dial in the choke behaviour to get the cold (stomp the gas, turn the key, drive away) behaviour the good-running, well-adjusted '60s cars gave.