black smoke from exhaust... what could it be???
 

A friend of mine has an Elantra 1997 and when pressing on the gas pedal and the motor rev. it brings out black smoke from the exhaust and he went to the hyundai for repairing they said the motor wasnt adjusted and they did adjust it and it's much better and moving faster now and everything is ok but still the black smoke comes out can anybody tell us what to do to stop that smoke ......