I've used Tamiya with good results doing the following for airbrushing:
1. I stir the paint thouroughly folowed by a good shaking for 1 min. to insure the paint and vehicle are mixed well.
2. For general spraying I thin 2 parts paint to 1 part thinner (91% Iso Alcohol) sprayed at 15 psi. For fine-lines I thin it at a ratio of 1:1 paint-to thinner and reduce the psi to around 10 psi or lower.
2. I test spray on a scrap piece of styrene, and when I'm satisfied with flow, coverage, psi and volume settings, I move on to the model.
3. I use an Iwata Revolution HP-CR gravity-feed A/B.
Hope this helps, Good luck!
Greg Williams
Owner/ Manager
Modern Hobbies LLC
Indianapolis, IN.
IPMS #44084