Carter AFB about to become a door stop...

I didn't see this mentioned, have you checked to see if the choke is opening all the way when warmed up, and staying open as the throttle is blipped? The heat stove in the exhaust manifold may be burned out/have a hole in it.

 

X2
This is more than likely your problem. On my 64 with a 401 and afb, I had the same issues.
The seperator plate was the issue.

 

Times 2 on this, have run across many weak coils over the years. Back in the late 50s/early 60s, would go to the friendly parts store and get a half doz or so. Take them them back and put them on our Sun equip and test and keep the "hottest" one. Rest back in the box and returned to be put back on the shelf to be sold. Nothing wrong with them, some are just hotter than others. Just another old racers trick. Have had many folks bring their car in for carb "rebuild", hook up the Sun diagnostic equip, yep about 90% of the time ign problems. Pull the dist, on to the Sun dist mach, new points, cond, check vac advance while setting dwell reinstall, check coil, time, adjust carb and away they go, happy as a clam at high tide. Fuel systems take some bad hits when ign is the culpret. PS: Carter is prob the finest, most reliable, maintenance free street carb you will ever find and it only takes one split to have it apart to look at if there is a percieved prob and they DONT LEAK/SEEP!!!. Good Luck!!!

 

Does anyone which manifold gasket is the right for this carb and engine combo? I hate the stupid yellow accel coil anyway so its going.