Hello mhastings,
Make sure the engine linkages are correct first. Do "The Llinkage Tour". These injection systems "wear" rich with age. But you need to find out if when your system is running rich. Cold, hot, at idle, mid range, high range,at acceleration or all of the above? Read about "The Split Linkage Test" to help determine if your system and when your system is running rich.
Yes, the thumb screw on the back of the injection pump is for low range fuel adjustment (idle and up to 1700rpms). It must only be adjusted when the engine is off and it is engaged by pushing in on the knob, engaging the slot and turning. It will "click" as it turns. The idle air adjustment is the large slotted screw on the intake manifold. Spend some time searching up the information on these items on this site. Once you determine what is going on, we can help you adjust the injection correctly.
The Pagoda Golden Rule.......... "Before altering the expensive and complex injection system, make sure you have a perfectly tuned engine, a tested WRD, a leak proof starting valve, correct engine linkage, and a clean fuel supply with adequate pressure and volume".