Currently, my two Throttle Positioner / Choke Breaker diaphragms have vacuum leaks - they've been shelved. Also, I have a non-smog Aisan 2F carb, it never came with the diaphragm, but, it does have the function on the choke spindle, with the torsion spring etc. I'm probably over-thinking it, but, it would be nice to source a vacuum diaphragm that isn't rotted; I've even considered adapting a replacement Delco distributor diaphragm to perform the function.
The way it is set up now leaves much to be desired. Here, the winter at 7,000'-above-sea-level challenges my non-smog Aisan. The amount of fast-idle is correct when the choke cable is all the way out, during start-up. But, after that, I need to manually crack the butterfly open by slightly pushing the choke knob in. When I do that, I loose some of the fast-idle, so there is a compromise between opening the choke to let the air in, and slowing down the motor. When it is really cold, I have to choke it more when I'm idling at an intersection, and choke it less when I'm accelerating, which is annoying. Formerly, my original factory equipped OEM USA-smog carb with leaky, but functioning, choke-breaker / throttle positioner vacuum diaphragm let the fast-idle be fast, but, it opened up the choke-butterfly with the help of manifold vacuum. I wasn't forced to use the choke knob in a middle-position. It didn't drop idle speed just to feed more air thru the carb's nozzle.
I'd imagine that a cable-stop on a choke cable mounted in the cab could perform the function of manifold vacuum. Its movement would be restricted by installing a Dorman 'cable stop.' It would be long enough to make the curve so that it pulls from the outboard-side of the carb.