Black smoke is unburned fuel hitting the exhaust after it has passed through the engine. Diesels need air and fuel to run properly, in a proper mixture. Change your air filter and you might get enough air to burn that fuel. When you really hammer it you probably will still get a little black smoke.

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1985 300D, 237k.
1994 F-350, 6.9 diesel, 5 spd manual, Banks Turbo. 261k.
Sold: 1985 300CD- 267K