OK, I started up one of the trucks the other day, and even after it was warmed up, with the choke wide open it was running very rich, to the point that I had clouds of black smoke coming out of the muffler and would flood out at low idle. Last time I ran it, it ran well.
Mixture screws were the same as before, and nothing else was changed.
Anything obvious to look for before I start disassembling the carburetor to look for somthing amiss?

Truck is 1960 F600, 292 V8, stock Holley 2 barrel carburetor with manual choke.

 

Sounds like you had a float problem. Float may be stuck or have a hole in it that has let gas inside it. Needle and seat assemble may be stuck open for some reason.

 

If it has been sitting for a while, you may have some bad gas that is causing the float to stick. Might try running some Seafoam through it, it will likely free up what ever is sticking.