Carb flooding

I have a 1977 Ford F 100, !/2 ton, 2-wheel drive, 4.9L inline 6, Carter YFA 1-bbl carb, 3-speed manual trans. I can't figure out why the engine keeps flooding. First start of the day it starts fine, choke operates correctly. I get onto the freeway immediately and drive 5 fwy miles to work. I pull into the parking lot, choke valve is wide open, no fast idle, engine at normal temp. I let the truck idle for 1-2 minutes and then it dies and becomes difficult to restart because it's flooded.

If I let the truck sit for 8-10 hours and try to start it (ambient temp 80-90 degrees) the carb is flooded from the get-go and is undriveable till engine reaches normal temp. I've replaced fuel filter, spark plugs & wires, cap & rotor; set timing, idle mixture & speed; freshened up the carb with a gaket kit & made all the adjustments. This problem has persisted with 2 different mechanical fuel pumps (one was new) and a generic electric fuel pump. I'm stumped!