Unlike gasoline engines which the driver throttles in more air, a diesel throttles fuel. Put in too much fuel and you run rich which can result in black smoke.

Watch this diesel rig BEAT a Ford Mustang on the drag strip: http://www.youtube.com/watch?v=-Kfd3A7KFko

Dynotesting diesels [note, mausok talaga]: http://www.youtube.com/watch?v=ox4cwo0bk1U