It could be some dried paint inside the nozzle. Do you have more than one that you could try?
If not, you could soak the nozzle in some lacquer thinner or acetone and probe it gently with a sharpened toothpick. Don't use anything metal. Use an eyedropper to flush it out.
Do you see bubbles in the cup or bottle when you spray?
How does the needle feel when you install it? Does it have a little drag?
Don