Sand blast gun

Had my HF blast cabinet for a few months. The gun is giving me fits . Clogs in a matter of seconds, maybe 5-10. Sand is dry ,screened. If I put my finger on the tip to blow air back wards it will unclog and blow sand again for about the same amount of time and stops again. Any suggestions for a fix or a different gun? I checked with Sears and TSC a couple days ago and they didn't have any. My old Sears hopper system works great with the same sand ,but then I have to do it outside and lose all my sand , not to mention peppering myself.
Yote
Is it clogged or is it cavitation. I have to re-position the suction hose often but works great other than that. I'm using 80-120 grit recycled glass.