super jet cavitation help???

my super jet cavitates on low end.i changed the pump seal thinking that was the problem but it wasnt, now im thinking its the pitch of the impeller? i have a 13/18 concord... anybody have any ideas? thx
 
This is my old ski I thought I had it fixed but didn't get a chance to ride it before I sold it. He has a 13/18 concord 3mm cutback impros prop with race prep. Wetwolf cone, stock nozzle. Jet dynamice intake grate. The prop has a few tiny hickys but nothing major. The ski is a limited ski with killer bottom end. When the prop catches.

Wear ring looked ok but I never measured it
 
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