Thanks for the helpful pictures, since those pumps look to be both rebuilt at some point in their lifetime it’s kinda a crapshoot what they have for internals. So I’ll give you a broad overview of what all is done to these pumps to perform better.
From top to bottom, late model cases (92+) have a preboost fuel adjustment, this is known most commonly as the “torque screw” this limits your low rpm fuel, counter clockwise gives you more fuel. Older cases do not have this adjustment screw, so they have max fuel available at all rpms.
Removing the governor rod, you have two springs that sit over the rod, the longer one controls your maximum rpm. Stretch the spring ~1” for an extra ~500 rpm. 2” gives you ~800. You will need to readjust your idle screw after this change.
Everyone knows the fuel screw on the side of the pump, clockwise is more fuel of course. Some pumps you will be able to turn more which generally means a healthier pump, often times this fuel adjustment is used in a rebuild to get a worn pump back within minimum fuel spec, but clearances are still on the loose side, so not really the right way to rebuild.
Getting deeper into the pump is the leaf spring you mentioned, you can crank down on the adjustment screw but if the pump has been apart by a rebuilder chances are you won’t have much adjustment here, and you won’t get much fuel from just maxing that screw out. I have a stage 3 leaf spring available that will pretty much max out that pump without major porting, or going to a 4 plunger design. Stage three leaf spring puts a pump in the 85-95cc range depending on rotor wear.
8 cylinder db4s are getting close to impossible to find these days, and a worth their weight in gold. Which is why I’m working on an in-line pump conversion for these trucks.
