I checked out comments for the wagner paint crew spray unit. One comment I found repeated was that the hopper needed close to two gallons of paint to work properly. While spraying with it today I got down to about 1 gallon of paint and the sprayer sputtered and was inconsistent. I took a ziplock type gallon bag, filled it with water, and placed it in the hopper. The pressure went back up and I had no further problems.
There are more old drunkards than old doctors. Ben Franklin