Mist coat, you should still see the underlying colour. You are correct to thin the paint so you can slowly build up the paint layer.
Assuming all the ingredients are compatable and not separating your paint in the airbrush, I'd suggest to practice on a scrap surface, even paper will do. Other things to try is decrease the psi, remove the needle protection crown to avoid build up of paint inside - that can spit out in clumps. Make sure the needle point isn't damaged, as that too can cause spitting. Also be certain the moisture trap is working, and no water is entering the airbrush proper.