It's not a problem with the needle size or the paints. I think it's what you are thinning it with and no matter what you use to clean especially windex will leave alot of unwanted stuff in your airbrush as windex forms a layer to help keep things clean. Start at the beginning and clean the airbrush in light soapy water then rinse in clean, spray with no thinning and if it goes gooey in the airbrush it's the paints or what's in the airbrush still. Mix the paint with your normal thinner in an old paint jar and see if it goes gooey then it's the thinner, if it's not gooey in the jar but still is when in your airbrush it's got to be what you are cleaning the airbrush with