The only thing that stood out (well 2 things) black/sooty plugs say the ignition is too advanced. Another clue to too advanced; coughing out the carb, when pushing on the throttle (gas pedal).
Coughing out the exhaust (during acceleration) is often either retarded ignition, or a leak in the exhaust.
If it were me; I'd retard the ignition little by little, and pull full to near full choke -- chevys are notorious for running lean when cold/first starting up.
HTH
Chris
