Thanks for the replies guys.
I think it is more of a grey smoke that comes out now, however it was black about a week or two ago.
I've not noticed any hissing sounds or groaning (only from the misses), so I'm hoping it is just crap in the pipes...
And is it normal to only have this smoke coming out when accelerating then?
What would be the way to get rid of old carbon deposits, my brother suggested high revs down a motorway...