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.
Welcome to the world of automatic chokes:
Poorboy has pretty much covered the bases but I will add my
Make sure you have 12V to the choke. Many will try pulling power it off the coil which may only be seeing 8 or so volts.
What Many don't understand is there are several things interacting to get the choke functioning properly.
1. Preload on the butteryfly when cold,
2. Choke pull off adjustment
3. Butterfly position once started
4. Fast idle cam position
5. Fast idle adjustment
6. How long the choke stays on
If there are no markings on the housing use a sharpie or scribe to add one to the main choke body (botled to the carb) and a few evenly spaced both directions on the housing that rotates
A critical part of the process is in RED. if a motor has not run for more than a minute an 8 hour cold down may suffice. More than that, I'll make the adjustment I think it needs and leave them overnight.
Other items that come into play are a bumpy cam, loose mechanical advance that may make it hard to get a stable "fast idle" setting
The higher the fast idle is set the more the butterfly needs to be opened by the pull off. This is due to the engine needing more air or it will run rich.
if it is open too far the engine will stumble due to being to lean.
With the throttle open a 1/4 way or so The butterfly should close all the way with a light forefinger tension required to open it. When the finger is removed the Butterfly should close all the way with a light tension I want to say snap shut but lightly so.
With the butterfly closed, close the throttle. It should stop about .100 or a bit more from the hot idle screw
Open the butterfly so a 1/4' drill bit fits between it and the carb throat. (simulates the choke pull off opening the choke on a cold motor)
Open the throttle slightly to release the tension on the fast idle cam and release the throttle.
The throttle should now stop about .060 or more from the hot idle screw (if the fast idle is adjusted correctly.)
Are we having fun yet?
One thing to keep in mind: the choke preload only determines how long the choke takes too fully open. it is the other adjustments that determine the engines behavior when cold.
it can be frustrating if you do not understand how all of the above interact. Loose mechanical advance or a lumpy cam will aggravate the process but can be worked around with adjustments and tweaking
This is a trial and error process that may require several attempts to get it right. Every motor is a bit different unless stone stock. Even then they may require a bit of tweaking from the factory spec'd adjustments Once done they are wonderful. I love to fire my car up at a show have it run on a slight fast idle, blip the throttle and have it drop down a bit, put it in gear and drive out with no stumbling popping spitting etc.
hope this helps and keep us posted
