Classic/Antique Car Repair: 1955 Cadillac Cold Start, external linkage, stop screw

Question
I have a 55 Cadillac with a 331 c.i., 4 bbl.  On cold start the car idles very slow, and rough.  If I attempt to give it gas wile cold the engine bogs down, almost to the point of stopping.  Once the engine warms, it runs very smooth and accelerates fine.

What should I be looking at:  choke, carburetor, heat riser?  I would think if a heat riser is frozen shut the car would run fine cold, and poorly when warm; which is just the opposite of what I am experiencing.

It seems as though when cold, the engine is either getting too much gas, or not enough?

Answer
It sounds very much like the automatic choke is not working correctly. With the engine cold remove the air cleaner. Open the throttle once and let it close. the choke plates should snap shut. At the same time the fast idle cam that the idle stop screw rest on should rotate it a higher step. If the choke does not snap shut the problem could be external linkage on the carburetor or internal in the choke housing. First try a can of spray carburetor and choke cleaner and spray the linkage on the outside of the carburetor. Do not oil the linkage as this will collect dirt and cause the linkage to stick. Work the linkage until it is free. Then holding the choke plates open with the throttle also open let the throttle close. The choke plates will remain open. Open and close the throttle and the choke plates will or should snap shut. If they do not then the problem is internal in the choke housing and it will have to come apart to be cleaned and adjusted.
Brad