SN revs but barely moves, is it possible for the prop to slip?

I have a 92 square nose with a 95 701 motor. I've been riding the crap out of it all summer long and it has been running great but recently its developed a problem putting power to the water. The engine seems to run just fine but it just revs without accelerating. Its an intermittent problem, sometimes it rides just fine but then sometimes I get on the throttle and it revs up but barely goes fast enough to stand on it. Its almost like something is slipping and the prop just isn't turning. Is this possible? Is there some sort of clutch assembly on these that can wear out? I did a search and found another member who was having a similar problem and it had something to do with a midshaft. What is that and how bad is it if I have to replace it? I'm still new to stand ups so I really appreciate any advice that you guys could give me.
 
Well I think I figured it out. The intake grate was hanging off the bottom of the hull. The plastic funnel right in front of the prop has cracked into multiple pieces. The edges of the prop are also dinged up a bit. It looks like maybe I sucked up some gravel or something. What do you call this plastic cone that the intake grate bolts to and how expensive are they?


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Location
NW
That's the intake duct/ pump shoe. Stock plastic is around $60 to $80 shopping around. Aftermarket aluminum Blowsion/ Jet Dynamics run around $80 to $90 but need grinding for proper pump seal and all mounting holes drilled and tapped for hull and intake grate. Aftermarket Worx racing one runs $120 with holes drilled and tapped ready to install no grinding on the one I installed. When installing your new pump shoe clean off all the old sealant scuff the mounting are real good and seal the new pump shoe with a liberal amount of 3m 5200 marine sealant.
 
Ok cool well at least I know what to do to fix it now. Is there a big difference in performance with the Worx intake duct? I'd rather not have to grind anything if I can just bolt one on. If there isn't much difference then I guess I should just get a stock replacement.
 
Location
NW
If you suck up any rocks / gravel the plastic ones tend to bust. If upgrade to a more aggressive aftermarket scoop style intake grate the added pump load will eventually break the stock shoe. The Worx intake duct is manufactured more precise and drop in. Not much of a performance boost over stock just a more durable part and possibly the last shoe you will install on your ski.
 
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