Lacquer thinner is pretty aggressive if there are any old deposits. If it seems dirty, disassemble the thing, makeing sure that the inside of the tip is clean as well as the passage through the center of the needle.
I have a Paasche H which I use for painting acrylics, mostly clear overcoats and tank treads, or with the large #5 tip for varnish. All in all, I think it is a really nice airbrush. Very easy to use and maintain. Even though it is a single action, external mix, it can paint a fairly narrow line. As a first airbrush, I think it is an excellent choice, and even as one grows to be skilled with an airbrush, it will continue to handle almost all if not all airbrushing needs.