I know how frustrating it can be.
Your problem, the sudden onset of it etc, sounds worse than i first thought and i am know thinking that it is a piece of trash gotten to the needle and seat. The needle and seat is under the nut/screw on top of the bowl - nut/screw are the adjusting means for the needle and seat. The needle and its' seat is the valve taht allows fuel to enter the bowl, when satisfied a float mechanism closes the needle and seat to shut off the fuel - exactly like the float on your toilet bowl and when they don't work right they can't shut off the water/fuel.
In a carb when that happen fuel will exit the top of the carb via the vent tube - they are at the leading edge of the venturii, the tubes that stick straight up. When needle and seat get trash in them fuel will flow out of the vent tube and mostly run into the engine flooding it and getting as you descibed black smoke.
With engine or fuel pump running you will be able to see it happen. It is very dramatic.
Don't feel discouraged, i am still working on the carbs i was grumbling about yesterday, i now have the plugs out for a look. These things are a challange, that is part of our attachment to them. If they didn't challange us we'd soon get bored and take up bass fishing.