There is a Facebook Group called: Kioti Tractor Tuning. One CK2610 owner commented on this subject.
"I adj. the fuel screw on the injection pump today and it made a huge difference! It woke the engine right up. The hardest part is getting the stupid cap off the adj. screw. I turned the screw...
Question about "The Screw"
Does the screw control fuel pressure? By changing tension on fuel pump pypass?
Or is this a needle valve changing flow rate?
I'm curious from a purely academic level.