There is too much unburned fuel in the cylinders, but its because the fuel system is screwed up. The engine is getting too much gas at some situations (acceleration), and too little in others (idle).
A carb with a leaking internal gasket, or a float level too high will let fuel drip into the intake when the engine is shut off. The gas can actually siphon itself into the intake.
A float that binds on its shaft, or dirt and crap from the fuel lines/tank will also cause the needle not to shut off fuel when the fuel bowl is full, thus the carb floods. Black smoke can also be caused by a sticking choke or an accelerator pump that is out of adjustment. Loose main jets, metering rods or fuel enrichment circuits could be out of adjustment or broken or plugged.
Poor idle can be caused by a bunch of things. Ign timing, plugged idle passages in the carb body, vacuum leaks in carb gaskets, any vacuum line, or intake manifold, or misadjusted carb can make an engine tend to stall at idle. The vacuum advance canister can go bad, the brake booster can leak, and the vacuum modulator on TH-350 and 400 trannys can cause problems if they fail.
good luck
chip
