I've never had trouble with the 2F non-USA Aisan, or OE 2F Aisan carb for cold starting. Just pull the choke, turn the key, and optimize the idle with the choke button, no gas pedal involved. The 2F does not like too much throttle on a cold day, fresh out of the stable. It needs choke at idle, but, it likes an open choke butterfly when mashing the gas in at a green light. I installed a choke cable, from my Weber conversion kit, to function like a hand-throttle, so I don't need a brick to operate the gas. However, my throttle linkage springs and what not kinda pull the choke button back in, or there there is too much slop in the factory throttle linkage, and it settles back down to rpm.
My non-choked idle was set at 600 in the summer, 100 rpm and much quiter than the 700 rpm Holley Sniper idle minimum.
I used to think that the cold intake manifold was the problem. Because engine coolant temp can be cold, but, if the engine ran within the last hour or so, the motor runs strong. The carb makes larger fuel droplets in the cold, and the primary barrel feeding the carb is all the way to the one side of the carb spacer. Sharp corners are less desirable than a laminar-flow. Running headers, cold intake manifold.
However, I'v never tested for vacuum in the cold. Running a cold 2F, there is a rougness, like one cylinder isn't firing as strong as the others, then it goes away. I wonder if the engine isn't sealing up like it is supposed to, on the rings side. I know the cylinders have wear, I can see it. The dry compression numbers were low, I didn't perform a wet compression test. The same cold-running symptom is observed when the plugs are fouled, maybe the plug fouls in the cold, and burns itself clean when warm?
My spark plugs are always getting fouled, but, I usually get to them before they make a roughness to the otherwise smooth-as-a-Singer-sewing-machine 2F. I never 'pump' or prime the carb with throttle (only tap the throttle when doing a hot-start), so it can't be flooding the intake from my doing, just the drip from the hot carb in the summer makes a puddle of fuel after the car is shut-dow. I think that oil-varnish is burning off of the plugs, oil getting sucked in on the intake stroke, via the rings. The plugs have a shadow of deposit, like only one side is really black.
The neat thing is most of my engine issues seem to be improving on their own. Oil consumption is not as bad as when I put the motor in service. I run the lowest viscosity oil that the Owner's Manual will spec. I always buy gasoline with additives, or add something to the tank. The latest Valvoline formula, Restore and Protect, is supposed to free rings of deposits - like an engine oil flush, but having anti-wear, and anti-friction properties, unlike an engine-oil-flush. I'm uncertain if the 2F soft seals are compatible with this synthetic formula. Lucas fuel injector cleaner, bottle of Techron, or MMO in the tank should also improve clean ring sealing, and I'm already on that track. Before the engine was on the frame, I had MMO in the crankcase for a month or so, it stripped the varnish from the lower half of the dipstick, but, I'm not going to stack-up miles with oil diluted with MMO, it will contribute to wear. I know that the rings are vulnerable, because oil in the combustion chamber is always a bad thing, but, the shiny black plugs that I once had to clean are no where as bad as they were when I first started with the always fresh and additive improved gas, fresh oil, and hand-cleaned spark plugs maintenance routine.
