Are you stirring the paint after adding reducer? If not, some createx paints are really thick and do not spray well. So if you're not stirring in the reducer you will clog up the airbrush. I use Paasche Talon's and the only time I have this problem is when (1) I do not stir the paint/reducer well enough or (2) when I let the brush sit for more than 5 minutes. I do all of my painting in my garage and when it is hot outside I will get more clogs due to the paint drying. As long as you keep a brush handy and pull the needle our every now and then to clean it you should be good.
In regards to thinning out the paint, I over reduce sometimes when fading colors and do not have an issue with paint drying, unless one of the situations listed above occurs.