Hard Starting Chevy

[swissarmychainsaw]

I have a 1984 Chevy Silverado; 305 ci 700r4 carburated that is hard to start.
125K miles on it.

Just did a basic tune on it, plugs, wires, dist cap. This did not change how it runs. It was a bit easier to start with the old stuff! Idles a bit rough, but once warm it runs great and gets 21mpg at 65mph with a 500lb motorcycle in the back!

Here's what it does:
After running the choke flap is perfectly vertical. (so I think the choke opens properly).
In the Morning I press the throttle down once or twice (same results) and the choke flap closes all the way.
Trying to start it though it chugs and huffs and puffs and bounces around, it spews black smoke (like unburned fuel) much to the happiness of my neighbors.

It looks to me like the choke is opening and closing properly, so I'm not sure what to do here. I'm tempted to just replace the thermostat on the choke, but it seems foolish to just start replace stuff I think works.

Any thoughts?

thanks!
--Nick