I don't like this thing I had part of it fall apart recently and I tried to re configure it so it wouldnt happen again and I frigged up my setting so I wanted to some ideas on how to lock out the lever and only the screw that is used on the older style pump to setmy idle.
You can't go to only the residual pressure screw for idle control as the spring that used to do the idle speed isn't there anymore in the 109 style pumps. There is a new idle spring that goes from the governor lever internally to a pivot connected to the "see-saw" on the outside of the pump. So you are going to have to use at least some portion of the "new" style idle control.
As mentioned above, you can disable its function by locking out the position of the see-saw, however to make idle adjustments you will have to turn 2 screws each with their own lock nut rather than just the one on the idle control rod. Kind of a pain.
The modern idle control is waaay better at keeping a constant idle speed than the old ones. It is much easier to work with really. I personally wouldn't get rid of it.