Take a better look at the carb as a whole. When your car is cold it is choked allowing vacuum leaks. After it has warmed and the choke is opened and idled down it can not tolerate bad vacuum leaks, thus it would stall at idle. I would be suspect of your vacuum hoses and or a faulty carb unit. Try spraying carb cleaner at your carb and vacuum hoses, if it causes your idle rpm to increase you found your problem. Do this when the engine is cold, to aid in it staying running as you perforn the test.