From the symptoms (idles ok but only if choke is almost shut, even when warm) its 1 of 2 things:
1. Clogged idle ciruit
2. vac leak at base of carb or intake
USUALLY it's #2
I've never had a "B" csrb refuse to idle - always a vac leak.
I guess a really "cruddy" one could do that but I'd look hard for a vac leak, usually base of carb, open hole, etc.
