Well, if your passenger side choke plate isn't closing at all when cold, then that will certainly create the problem you describe.

When the engine is completely cooled down, floor the pedal to engage the choke. Try loosening the choke housing cover.. if your lucky you have screws on the choke cap not rivets. Don't pull the cover off yet, just loosen the screws enough so you can rotate it. Rotate the cover until the passenger choke plate is 1/8" open (mostly shut). Tighten down cover and see if problem goes away. Make sure the palte still opens up when the engine warms.

See how that goes..

Scerb