You're probably asking too much of your engine and it is going through its knees. Because of the larger props revs are probably too low in relation to the torgue curve (your engines characteristics) and you engines governor is trying to correct that by pushing more fuel in the engine than it has oxygen to burn. Hence the grey/black smoke; lots of unburned fuel and other nasty stuff.
If the problem was there already I would suspect the injectors; all this assuming it is a diesel of course. Yep, Volvo's are diesel....