Adding a little info to this thread just "for the record" in case someone else experiences this problem.
I pulled the plugs to give them a quick read and they were very black and sooty. I gave them a good clean with a wire brush and brake cleaner and reinstalled them.
I then pulled the air cleaner off, gave the choke plate shaft and throttle plate shaft a nice spritz of carb cleaner just to ensure there wasn't any gum/varnish making things stick. There didn't seem to be any . . . I also sprayed down the heat riser linkage and throttle linkages.
Leaving the air cleaner off, I checked operation of the choke plate. It was smooth but there is a point in travel where it's a bit tight or "springy" - I don't remember if it was like this after I rebuilt the carb last year, but it seems to be "normal" and part of how it actuates when you depress the gas pedal to the floor in order to engage the choke. Experts, please feel free to correct me if I'm wrong.
I then started the engine, and choke plate was fully closed. Upon start up, the choke pull-off opened the choke plate slightly, as expected. The engine began to warm up, running with what I think is that characteristic "lope" of a cold big block running on the choke. As it ran, it started to slow a bit. I'm not show if the choke plate is opening properly yet, so I gave the throttle a little blip, and the high-idle cam seemed to move from the high setting to the middle setting. The idle sped up again as the engine got more air. After a short time it started to slow again, so I blipped the throttle again and this time it went to the lowest cam, I think it was on just the regular idle screw at this point. The idle seemed a bit low, so I held the throttle open slightly and that helped, so I screwed the idle screw in about an 1/8th of a turn.
I think the real issue is just the fact that instead of getting a proper warm up with the carburetor linkages getting a normal workout from driving, the car is just sitting in the driveway, idling. So, that being said, I'm going to just go drive the car for 40 or 50 miles and put it through it's paces. I did take it to the gas station and put 20 gallons of ethanol free 91 octane in the tank, so a long drive will certainly burn off any of the gas that was put in the tank back in October. (I can't see how gas could be too bad after just 3 months.)
Anyway, to summarize, there might be a slight issue with the choke operation causing the car to run rich, but I think it's just a matter of it being a bit tight and sticky after sitting for three months, and a good long drive should get things back to the way they were.
