Possible blade lay back can cause the water to not remain "loaded" on the blades as long. Yes, cups removed or washed out can do the same thing. Some times these things are not easily noticed by the naked or untrained eye.
Brett
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Brett Anderson / BBLADES Professional Propellers
920-295-4435 http://www.bblades.com/
looks like they'll be coming to you after the season for a little love...
on the other hand have been wanting to try Tempest and Rev 4s on the boat, what pitch of each would i need if my stock 21 Mirage Plus had me dead on for RPMs(6200-6300) and do you have some trial props available in these pitches, I'll need Left and Right