My first airbrush was a Iwata Double Action. I was advised to buy the best airbrush I could afford and I am glad I did. The double action required more of a learning curve (so I am told, I wouldn't know since I never used a single action) but my modeling results improved almost immediately. Being all metal, I flush with acetone. I have been doing this for over a year with no negative results to my airbrush. If you have a hobbly lobby in your area, you can use the 40% off coupon they occasionally put online and save quite a bit of money. Bubbles in you cup or bottle indicate that you do not have a good seal on the painting end of your brush. It takes pressure to push paint through the orifice so if you do not have a good seat, air blows back into your cup. Spitting paint is usually caused by several different factors:
1. Paint is to thick. Should be the consistency of skim milk. A good test is to take a toothpick and dip it in the paint and drag it up the side of the mixing cup. If the paint does not run off the toothpick and down the side of the bottle, it is probably to thick.
2. Paint is drying in the nozzle or on the needle. (with the pressures you are spraying with and if you use acrylics, this would be my guess)
3. Paint has dried gunk in it (You know, stuff that falls out of the threads, dried paint from the lid or the sides) plugging your nozzle.
I have had trouble with all three. Part of the learning curve. The first just takes alittle practice. The second is easily fixed by either getting a compressor with a regulator or purchasing a regulator. I spray between 10 psi and 20 psi depending what I am doing. The third is also easy to fix. I wipe down the lip of the bottle every time I open it, I use a disposable eye dropper to transfer paint from the bottle to the airbrush taking care to only get paint from center of bottle, and I never shake my bottles. I bought a electric paint stirrer from Squadron and I love it. I hope this helps.