I don't know how Tamiya Enamels are, as you can't buy them here, but if they are like any of the other enamel paint here, like Model Master, or Humbrol, normal thinning is about 80% paint to 20% thinner.
Possibly 75% paint, to 25% thinner, but you shouldn't have to go any thinner than that.
As well....what kind of thinner are you using?? I am assuming that since Tamiya has thinner for their acrylic paints, they must have one for their enamels as well, are you using that??? Have always gotten my best results using the thinner for the paint that the paint manufacutrer provides, Tamiya thinner for Tamiya paints, MM thinner for their paints, etc, etc, may cost a few bucks more, but the end result is well worth it.
25-30lbs of airpressure on your compressor??? You shouldn't need any more than 10lbs to airbrush with, I usually spray at around 5 to 8 lbs, pretty much all you need.
Where you live is it fairly humid??? If it is a watertrap on your airline is a must....although if you are using enamels exclusivly, the water won't mix with your paint, but you could still end up with water droplets on top of your paint.
As well, does your compressor have a tank??? If it does, does it have a releif valve on the bottom that you can open?
When you are done airbrushing for the day, you should open the relief valve on the bottom of the tank to not only relieve the air pressure, but air underpressure will have condensation in it (hence the watertrap on the airline), but if you don't use it for awhile with the air compressed in the tank, the water will lay in the bottom of the tank and will rust it out, then you need a new compressor. If you compressor doesn't have a tank you don't have to worry about it, but you should still have a water trap.
