First, your gun is using more air than the pancake compressor can generate, so its overworking. You need a bigger tank, bigger hp motor.
If you would set your pressure down alittle, the motor will not overwork as Much, but this is not your problem.
Too, many paint dealers will state which paint line will shoot better than others. for example, SW makes three exterior basic paints. The top of the line, super paint, will not shoot good in rigs, due to its vescosity or thickness, they recommend A-100 for spraying, its thinner and just does better.
You might check if you have the proper spray tip. you could be using too big of an orfice and there for not picking up paint.
If the rig is not new, you could have packing problems. This has to be done periodically to change the packings because of clogg ups.
In summary, I feel that your problem is pressure, tip size, paint thickness, and packings.
Just my opinion, I would have to see it first hand to make a better determination.