AD41B lack of power and black smoke

I have a pair of AD41Bs in 31 foot Portefino. In neutral engines rev ok without any smoke. When accelerating the port engine will not pick up and leaves a carbon slick on the surface with thick black smoke. After a while, gradually accellerating, the engine will pick up and the boat will come onto plane with no more smoke. It then runs fine until the throttle is shut and the boat slows then will do exactly the same again when trying to accelerate again. I have removed the injectors and had them serviced and have replaced all the filters on the engines but the problem still persists. Does anyone have any sugestions please?

Check for air leaks on turbo pipes. check boost pressure. these KKK turbos can suffer corrosion on the back of the impeller housing, this acts as a brake on the turbine. Remove air filter and check turbine spins freely. I have also (rarely)seen these with broken shafts so check that too. Injector pumps can also give problems so as a final check, get it tested at a diesel spe******t

Thanks for reply. Forgot to mention that the first thing I did was to get the turbo checked and it was fount to be fine and it spins freely now. Havn't checked the boost pressure but will do. Also the injector pump could be checked but I presume it will have to be removed to do so. Do you know if the valve clearances could cause this sort of issue if they are not correct? Trying to cover all the simple possibilities first.

Tappets can cause this but as both engines should have had tappets done at the same time, it is unlikely to effect just one engine.
If turbo has been checked, you could have aquired a damaged "O" ring on either end of the link pipe between turbo & intercooler. The one at the turbo end is quite thin and easily damaged.
Pump need to be off and on a test rig to check. Not a DIY to re fit as timing needs to be set- That's why I put it as last choice. Good luck

Hi jeff

Sounds like sticking turbo, recommend fitting a boost gauge to the inlet manifold and sea trailing, should see boost from 15psi to 20 psi running constant with throttle wide open, if not then a replacement turbo is needed, hope this helps, let me know how you get on