Trying to get our second ski up for the coming season here and over the last 2 years we have had trouble with the ski cavitating at 4k rpm just like a switch its there for about 100 rpm up and then its gone and the ski returns to normal.

I checked and the only thing I can come up with is that this boot is not tight, I can pull it back with about 3lb of force. I know that if air gets in there it goes right down to the impeller and can cause cavitation.

Here you can see the boot I am talking about:

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And with a little bit of force I can pull that boot down:

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Can you guys / gals confirm that this is the problem or can you point me where to look next.

Thanks in advance!