Black smoke is fuel, way too rich. The carburetor is flooding, probably from a piece of trash under the needle valve. A leaky float that is partly filled with fuel will also cause flooding. The engine is probably difficult to keep running at idle, right? Blue smoke is oil, and white smoke is coolant. You probably need to give the carburetor a good cleanout, and install a good-quality inline fuel filter between the fuel pump and the carburetor.
Jerry
