Yanmar 6LY smoking - any ideas???

[Arcee]

I have a 315hp yanmar that is blowing lots of white, maybe blue smoke when cold. It then reduces a bit when up to temp but is still there. Then when up on the plane, 2200 rpm and above, there is sign of black smoke. Its a bit hard to tell because of the underwater exhaust but definitely looks darker. The engine sounds fine, maybe a bit of tappet noise.
I have cracked each injector one by one and there is a noticeable change in tune with each one.
Also have just had the injectors serviced by a reputable technician, new nozzles etc.
I am looking for some tips before chucking a whole lot more money at professional attention.

- Richard