I'm having a similar problem with paint clumping on the needle point (past the tip). Wiping the tip with a cleaner soaked q-tip or rag takes the clump off and the brush can be sprayed again. More often this only helps temporaraly and the paint begins clumping again.
I can kinda deal with the paint clumping except before it's visible as a clump it starts effecting the point where the paint flows as I pull back on the trigger (badger anthem 155) making it difficult to predict exactly when the paint will begin to flow (goes down fine when it does come out).
I've tried varying the amount of thinner as well as pressure (polly s acrylics typically 60/40± @ 12psi). I clean the airbrush thoroughly after each use. My first thought was that the metal needle was so clean that the paint would immediately stick and begin building up through use (I spray for about 15 minutes a go interspersed with multiple tip-cleaning sessions).
I was wondering if the above mentioned needle lubricants were suitable for deterring this kind of build up. Do they provide a protective bond on the metal or are they just lubricants as their name implies?
I'm not even sure I'm on the mark with my troubleshooting and would sure appreciate it if somebody could stear me in the right direction.