Could be overload by a wrongly sized propeller or a fouled propeller inducing to much load. Is it smoking black also out of gear if you rev up? Could be clogged injector nozzles then
Two out of three answers are correct,Dont know
S######n, ?
Try the air filter first,Check timming,running temp, All cheap Then I`ll take your money to calibrate your injector`s
I have a volvo 2002 and used a can of injector cleaner in a teankfull of diesel and the exhust is now completely clear. Its costs about £8 which is much cheaper than servicing the injectors to achieve the same thing.
Treat the deisel with biocide regularly and the injector cleaner once a year.
use starbright hull cleaner to remove the stains. It works brilliantly