[Slimlavud]

Hi
I have a 1995 940TDIC auto wagon, in UK, 100,000 miles, bought recently with no history. It runs very well and uses almost no oil and water. When I had a good look under the bonnet (hood), I did notice a peep of red Hermetite gasket compound around the head gasket... then I found two of the special socket adapters for the head bolts in the luggage compartment at the rear... then I decided to stop worrying... it runs well.
But, someone has had a fiddle with the fuel screw on the pump, the one that regulates the stroke of the plunger in the pump.
The car starts instantly but does smell a little of diesel (but no leaks) and smokes a bit on hard acceleration (black smoke that does clear if I push it a bit), how should I adjust this screw please? It makes around 24 to the (Imperial) gallon around town driven very gently and gets well over 30 to the gallon on a run.
Thank you
Simon