http://www.AsktheBuilder.com founder, Tim Carter, demonstrates the Rockler HVLP paint sprayer showing how it works and how easy it is to clean up after use. This is another rockin' tool from Rockler. I coined that phrase and I sure hope they don't steal it! :-)
You must just keep thinning the paint until you get it right. With each test, you MUST get rid of the not-thinned-enough-paint out of the uptake tube and inside the gun.
You may have to clean it out several times until you discover the correct viscosity.
The following link is how to use a paint sprayer: http://www.askthebuilder.com/how-to-use-a-diy-spray-painter/
Tim reviewed another paint sprayer here: http://www.askthebuilder.com/wagner-flexio-890-spray-painter-review/