I recently bought the GX 19 sprayer and started using it to spray enamel on cabinets. The enamel I use is thick and sprays fine through this sprayer, even when dialed down to 1,000 PSI. I've never used Styx primer, but the primer might be too thick for your setup. There are a few things to check. It's possible you're spraying with the pressure too low or using an FFLP tip that's too small. You didn't mention the tip size you're spraying it through, but you might have to use an FFLP tip with a larger orifice if the primer's really thick. Make sure the gun filter isn't clogged. You might also have to use a different size mesh filter in your spray gun. The GX 19 comes with a 100 mesh filter, but you might have to use a 30 mesh filter. That could be the reason the primer's tailing, or the primer's too thick, which you could try thinning or use different primer.