Volvo Penta Emitting Black Smoke

[liomshe1]

hello.....i have a volvo penta md7a engine.....the injectors are new the pump is in good condition.....oil has been changed ....air filter ok.....no problem starting....in fact this engine has been referred to me as running like a mouse heart....it is so silent and no problem pushing the boat.....but when i push the trottle forward black some appears and gets very smokie .......can anybody assist me in solving this problem please ........thanks Liam