I suggest that you go to http://www.perrypumps.com and read the instructions that you can download there.

Note the damage you can cause if you move the pressure adjustment screw too far in or out. I suspect this is a major reason for peopel who have problems. Most of the time the screw is fine where it is. The pressure is not that differant than muffler pressure with a fairly restrictive muffler, however with muffler pressure the pressure drops at idle, but stays the same or nearly the same with a pump. Because of this there is no way the needles, especially the low speed, can stay the same.