I did a quick search and did not find a post that talks about this very problem. The guy figured it out and posted pictures. I don't remember the exact details but it seems like a port was partially blocked that he filed out.
edit: found the post. His problem was with the gun on a HF blasting cabinet, not the pressure blaster. Guess my old memory let me down again
http://www.garagejournal.com/forum/s...ad.php?t=88862