As already mentioned, turn the ball valve on the center rack to 1/2 closed.

i fought jumpy rate control on my 1997 854 as well. It turned out to be the flow meter going bad. I caught it by setting the rate in manual mode and watching the flow meter pulses on the Ag Leader system that is running my sprayer. With a fixed flow rate, the flow meter pulses should have stayed about the same. Mine were jumping around quite a bit. A new flow meter took care of the issue.