i would think that a vacuum problem would be more evident when warm,not cold and just starting. are you certain that you have a vacuum leak at all? are the choke cables working correctly and not slipping in the sheaths? did any one check compression? has anyone adjusted the valves and possibly has them too tight? is the vacuum assy on the distributor working properly. i seem to recall two vacuum ports there. is the breaker plate in the distributor returning properly? has anyone check the carb diaphragms? how about the throttle plates for leaking and sucking air? are the intake nuts tight to the head? upon start up, does one carb piston ride much higher than the other when idling? if so,most likely in carb,throttle plate leaking or bad diaphragm. possibly worn throttle shafts but worn shafts usually caused fast idle when warm.. make absolutely certain that choke cables are working properly, engaging and releasing both chokes.