I have a Mercury Villager 1996. When I start the Van sometimes it starts right up but if it doesn't the I have to keep cranking the starter until it catches and then keep my foot to the floor until the engine smooths out and the exaust spits out a cloud of black smoke. I have had it to 2 different mechanics and no one can figure out whats wrong!

HELP

Optional Information:
1996 Mercury villager