To answer the original question, I'm not sure why it won't spray unless the nozzle or air pressure isn't adjusted right but I don't know much about spraying finish except that back in high school shop we wasted all our time making gear shift knobs and then sprayed about 16 coats of lacquer on them at one coat a day. The nozzle could be plugged and the spray gun has a pressure adjustment as well as the compressor has an adjustment.
Another ditto to John although when I saw that post last night, I wondered what you have to do to make it that way. I then saw the drugless post and I have to say that that thought crossed my mind also. Harking back to gutterless(here we go again) made me want to rule him out as the drugless poster except that I couldn't do that when I realized that it wasn't signed drugless and sober. I also have been reading recently that poly is better when not sprayed.