Lawn mower has black smoke coming out and starts up and then immediately shuts off?

One of two possibilities for black smoke and not re-starting: (1) the spark plug is fouled and not providing full ignition to the gasoline thereby allowing the engine to flood = nned to clean or change the spark plug (2)carburetor needs adjustment(s) = the float may be stuck in the open position; the linkage may be off and not allowing choke to open clompletely; the needle valve(s) may have vibrated to a more open position.