Choke adjustment....DGEV

Every morning after starting my 73 GT it leaves LOTS of black soot on my garage floor. It comes out mixed with condensation right after startup. My son (who drives the car) starts it and lets it idle for about 4-5 minutes before he leaves for school. Temps have been in the high 30s and low 40s here, at that time of day.

My question is.....should it be doing this??? I have checked the plugs after driving it on the freeway when fully warmed and they appear to be normal, light tan, no buildup of any kind. I'm wondering if my choke is engaged too much.....maybe at startup its running too rich too long????? The present (right now at 11:30am) temp here is approx 55-60 degrees......if I adjusted it in that temp to where the butterfly was JUST closed and did not rotate the housing any further would that setting also be appropriate if it was colder outside?? The butterfly does open fully when warm but I'm wondering if it takes to long to get fully open.

Any help appreciated.
Mike