It sounds to me like the choke setting is not done when the throttle is set on the fast idle cam. There may also not be a functioning choke pull off, or it is not opening the choke blade as much as it is suppose to. It also sounds like the fast idle speed screw may not be adjusted correctly.

It sounds to me like nearly all the adjustments are incorrect.

With the motor off and still cold, open the throttle about 1/2 way, and manually close the choke blade. This should lift the fast idle cam up so that when the throttle is released, the fast idle screw should be on the 2nd highest step (some are the highest step) of the fast idle cam. If it is not doing that, the rod to the fast idle cam needs to be adjusted so it is correct. There is a designed fast idle speed the fast idle screw is suppose to be set at (read the carb's directions).

With the throttle on the fast idle step, and the choke blade manually closed, the choke housing is rotated so there is enough tension on the choke blade to hold it closed. On a very cold motor, that tension could be pretty strong. There should be markings on the choke housing that rotates that identifies the "normal" choke tension setting, plus marks for a more lean choke or a more rich choke setting. Start with the setting at the normal position. Generally chokes function best below 60 outside degrees. All the choke adjustments have to be made on a cold motor. You can not properly adjust the choke if it is not cold, it will nearly always be set too lean and will open too fast

The Choke pull off should open the choke against the housing spring pressure about 3/16" to 1/4" (there is a drill bit index number for this setting between the choke blade and the top of the air horn. That adjustment is a starting point and the clearance is achieved by bending the linkage to the choke pull off). if it opens too much, the choke is too lean. If it doesn't open enough, the choke is too rich. Properly set, the motor should not run rich nor lean. The choke pull off has to be made while the motor is cold (if the choke pull off is vacuum operated, the pull off clearance can be done with a vacuum pump before the motor is even started). Once the motor warms up, the choke pull off adjustment has to wait for at least 8-10 hours.