I think this thread answers the question pretty well.

One of our members used 4 separate medical syringes, he fitted an internal spring to give resistance.

If you really want to why not turn each screw in until it is closed counting the number of turns for each screw, use a notebook to make notes or drawings, then turn each screw 1/2 a turn out. If that don't seem right turn each screw 1 full turn out. Road test each setting.
Have you checked the small "O" ring on each adjuster.

Trial and error I know but you will get a good idea if it is the problem.