Ford Repair: running rich, k n air filter, fuel mixture

Question
I have a 1990 ford mustang 2.3L efi . It idles smooth and runs great but the fuel consumption is horrible about 4.5G/60  miles( 16.2L/100km).  There is also black smoke in the morning when I start it for about 5 secs. Is the engine running rich and if so is there a fuel mixture adjustment or anything that I can try to fix this? I have already replaced the K&N air filter ( saved it )with a new paper filter and had no luck. Any help would be appreciated, Thanks for your time.

Answer
hey there, i think there may be a problem with a leaking injector, or injectors, black smoke on start up indicated a rich run! but if it is in the moring then it sounds like an injector is leaking down into the cylinder, If it has a harder start, or extended crank first thing in the moring befor all this smoke, then i would  definitly be leaning towards replacing the fuel injectors,
Good Luck
Chris