Well, it seems with that style airbrush (especially if you use primer with it) you should pour some thinner ( I use 99% isopropel alcohol) down the back to clear the back. If it's cleaned and properly thinned, and mixed, i'm not sure what the problem could be. When I have that problem, it usually gets fixed by adding a little thinner, and a proper amount of mixing. You could try putting your finger over the end to block the airflow and push the clog back into the paint chamber, though it won't fix the problem, it'll work better temporarily. Again, more drunk than before, and certainly not an expert =p