Painting Thin Line Troubles...

I have a tricky issue. When I attempt to airbrush a fine line of paint, the paint stops its flow shortly after achieving the line thickness of desire. Once my original sized line stops flowing I can widen the line thickness and the paint flows some more, then stops again. I can repeat this several times all the while the paint line widens little, when in actual fact the airbrush is set for a much thicker line. After this procedure is repeated yay amount, all of a sudden a large burst of paint comes out which is the line thickness that the airbrush is set to.

I usually airbrush with acrylics and my airbrush is a single action piece.

I think the paint is drying inside my airbrush; this is the only thing I can think of that could cause such a problem. Is this correct?

What possible solutions are there to this dilemma, or is there any? Or perhaps Enamels, with the slower drying time are a better paint for the airbrush?

Thank you for any help!