back to the gun ....
If your gun does require 12 CFMs then it may not work with that 1/4" hose. However, my HF purple gun runs fine on 50 ft of 3/8" flex hose, the green one, but internal openings in the quick change fittings are 1/4" ID.
Please verify that the gun is the one Rick suggested and requires 12 CFM.
If you want to try that gun, use a larger supply hose if you can. Eliminate the QC fittings if you can. I had a flow control issue until I adjusted the air volume at the base of the gun handle. Hold the trigger in until you get good atomization and a wet coat pattern while you adjust the air flow. Then raise or lower the pressure at the gun regulator in 5 lb increments to see if that helps. If not, I suspect the gun is the issue.
FWIW, I don't use a viscosity cup, but I know from experience when the mixture is thin enough ... more or less. Water like is too thin, milk is about right in my gun. :smile3:
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)