Running rich 2.0L Petrol

[stuc]

Hi I suspect my 2L petrol is running rich, after a colleague noticed a strong smell of fuel while driving behind on a bike.
i have checked the air filter and it looks ok.
Plugs are quite sooty.
I think it is very heavy on fuel, I dont expect 30mpg but I was hoping for a bit better.
Is there any way of adjusting the mixture?