Sounds like either too thick of paint or not enough air pressure. These two can be interchangeable. Watch some videos on thinning paint. I like mine about as thick as heavy cream or half and half. Air pressure to the brush will vary between 20-40 psi. Really watered down or thin paints will use less air pressure and thicker syrupy paints will need more. I find I tend to stick to about 30psi these days. I like to thin with a little 90% alcohol and createx thinning solution, but water will do in a pinch.