I wouldn't touch a thing here, unless your car is running poorly. The knurled knob that wbain refered to (on the back of the injection pump) is the idle mixture screw. It shouldn't be touched unless you have reason to believe that it has been tampered with. Like the fellow said, do NOT adjust that screw unless the motor is OFF. If you do move that screw with the engine on you run the risk of stripping out the interior of that setscrew. The other big screw on top is the air inlet screw and is used to adjust engine idle speed. There is a way to determine if your rack is stuck. At the very front of your injection pump there is a rubber/vinyl cap that covers a metal disc. This is about the size of a quarter. Once this rubber grommet is removed you can stick a small probe into the hole and with a small push you can move the regulating lever (rack). It should move fairly easily, if it doesn't you can squirt lubricant in there to see if you can loosen it up. However, if your car is running well then don't touch any of the controls on your injection pump. Just run a can of good injection cleaner through the fuel system and that should do it. Cheers.
1967 Jaguar E-type Series I, 2+2