300 TDI de-tuning

I think my 300 has been "tweeked" as it pulls like buggary when towing 2.8ton it throws out alot of black smoke and is doing 13-14mpg!, and getting through 2 -3 tanks aweek, expensive to run. Have read somewhere about adjusting the tension of the spring under the diaphram in the top of the pump to increase power, have tried undoing this,had no effect, as the end of shaft is offset, does turning the diaphram allso effect power?, is there a standard position it should be in?
JD

do a search on here, there is a thread linking a few sites on the procedure of tuning a 200/300 engine. maybe tht would help. to be honest though towing a cable percussion rig cant do the MPG much good! whats your company name? we might have used you before

not sure if i know anyone in bristol, a bit ot of my area!