What happens if you nurse the RPM long enough to get up to normal coolant temp? It sounds like you've got piece of debris somewhere in the idle circuit. I've cured a problem like that by revving the engine up and putting my palm over the air horn to draw liquid gas through all the carb passages- - - -sort of a power flush with liquid gas instead of vapor. Let the engine catch up to avoid a flooded stall by clearing the airway and opening the throttle a little more. Repeat as required.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!