I'm not sure who you are (don't recognize your screen name) but regardless, here are a few possibilities:
It could be your choke or choke linkage (divorced electronic choke in the intake manifold or a Superquad with the integral choke?) sometimes newly rebuilt carbs will require miner linkage adjustments where new plating or R&R causes a tight spot somewhere, also be sure that when warm that the choke is all the way open. Look for stick spots and adjust them or add a tiny bit of lubricant to see if it helps.
If the carb is a 1972 or later TQ there's a chance that the fuel bowl seals are leaking fuel or that you have a sunk or bad float. If this is a carb I have recently restored these two possibilities are unlikely as it was test run before it was shipped and those issues are pretty rare once they have passed a run test. More likely is a fuel contamination issue and not a choke issue. Black smoke is an indicator of fuel dumping in at an uncontrolled rate, a stuck needle and seat from old gas/garbage is a common problem if you put a newly rebuilt carb on an older fuel system (old tank, fuel lines, fuel pump that might have rust and debri in them, etc.). It could also be a venting issue should the rubber vent lines on you TQ are failing or improperly routed. How long has it been sitting since you installed it?
If you get stumped and need further help feel free to give me a call, thank you for your business!
