With the new thinner, thinning Model Color, I start with 3 parts thinner to 1 part paint, and go from there.

Some colors need a slight more thinned (any with heavy pigments), but 3to1 thinner to paint is a good start. Air pressure normal about 15-20psi.

Has never given me a problem using it this way, but I have been using more and more of the Vallejo air when airbrush, just simple drop it in your airbrush and go.

As well, if you are mixing in your airbrush, put your thinner in first, that way the thick paint isn't sitting down on the tip of your needle, which will never get mixed, and clog up your AB. I generally go thinner, then paint, and then back flush to mix.