You already have some good suggestions there so I can't add much except that you may have a clump of paint in your airbrush or it was not cleaned good enough. In regards to 40 psi, that is not too high if you are spraying one color such as a car paint job.
Us T-shirt artists spray at between 60-80 psi on hard materials such as license plates and helmets without any problems.
Spraying at higher pressures does cause overspray to be a problem with more precise paint jobs like camo patterns, but paint does atomize better at higher pressures.
If you are getting spatter at 40 psi then cutting down the pressure won't help. You either have to thin the paint and lower the pressure or find the obstruction. Did you strain the paint first?
Are you using the #1 needle and tip or the #3?
Mike
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon