How to adjust injection pump on a small cam cummins

Not for idle speed. It is for throttle leakage at idle. The amount of fuel allowed to flow past the shaft at idle. The other screw is the wot throttle shaft stop. You only need to adjust the throttle leakage screw if the engine gallops when it returns to idle. Meaning it drops a little below idle and then goes back up to set idle. Playing with that screw also effects the return speed to idle and screwing with it the wrong way can mean the engine will return to slowly or not have enough fue flowing thru shaft at idle.

The actual idle speed adjustment is done thru the 1/8” pipe plug on the bell shaped housing the button snd springs or in.

 

Adjust for more horsepower ? It should be calibrated by a shop. Tell them what you want and they can calibrate it so it all will match. But if want to tinker with it at your own risk, you can get a stinger for full fuel or change the button inside and the spring (Stiffer is better), I can’t remember the color spring I had in mine, it was from a KT Cummins, think it was purple and yellow IIRC. All this you can achieved by removing this bell cap as @SmallPackage said. It’s all in here.

 

You can also change the gear which is above the bell cap, looks like a block right above the arrow.

 

Search for a reputable Cummins pump shop. Someone who knows how to play with them and adjust them to your liking, but be warned, your playing at your own risk, everything should match, including injectors and turbo, more fuel needs more air. I played with my Big cam for a bit, until I found someone who knew how to tuned them up. Thats how my pump got calibrated (over 300 psi) and bought a set of matching injectors(top stop backed off) and added the Holset HT 4(or was it the HT 3, been so long I can’t remember)turbo on it.




EDIT: There are more members on here that know a lot more than I do. I’m just a driver .
@SmallPackage and @OLDSKOOLERnWV for starters.