It sprays water fine with the cup in place but not paint?. did you filter your paint.
yet you say it doesnt pulse with water
what paint are you using and how much thinners have you used
ive just dicovered that the gun uses a massive 12.5cfm air so is your compressor up to it what cfm is the compressor
or it could be that your regulator or airline isnt delivering enough volume of air to keep the syphon steady some regulators wont let 12.5 cfm through
it could be the regulator or airline
when the comp is full it will run the gun but would not run it constantly as the pump wouldnt keep up.
if you could try the gun on another set up just to check its not the gun or
remove the regulator (just to test it) let the compressor build up to around 50psi (no higher) and try the gun that will tell you if the regulator is restricting the air needed
it could be the regulator or airline
when the comp is full it will run the gun but would not run it constantly as the pump wouldnt keep up.
if you could try the gun on another set up just to check its not the gun or
remove the regulator (just to test it) let the compressor build up to around 50psi (no higher) and try the gun that will tell you if the regulator is restricting the air needed
good you got it sorted
before you bought the new pressure switch did you try to adjust the original switch ?