93 running rough

[DieselNasty]

My buddies truck is not running right. The symptoms are as you drive the truck and you get on it and it spudders and it doesnt want to go. Then get off the pedal it spudders and almost seems to almost stall. I know that it is idleing slow and I have to adjust this, could this be the problem? Also we have done some modifications to the pump like a missing fuel delivery rate pin and we turned in the fuel screw a good amount. To adjust the fuel screw we used the advice to adjust the idle down then turn in the fuel screw. Is there a point were the fuel screw is not to go in anymore?

Could there be any other problems like water in the fuel or bad fuel because the truck ran good about a week ago and only kind of spuddered a little soon as you let off.