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My RPM's are norman and even higher but I'm down about 10 mph.

How to change a Berkeley jet pump impeller?

I own a 20 foot jet boat with a 455 cubic inch Oldsmobile engine. My engine's RPM's are norman (and even higher) but I'm down about 10 mph from 52 mph to 42-45 mph. I believe it may be my impeller that is starting to wear out.

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This is a shot in the dark BUT check to see if there is a wear ring that would sit around the outside of the impeller.Its inside the pump but would be right where the impeller spins.Jet skis have them and I thought yours may also.Hope this helps

Posted on Jul 12, 2010


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2011 seadoo boat 150 speedster surging up and down on full throutle but idles fine in neutral and changed the plugs and new gas and tps sensor and still no differnce

Check for air leaks on the manifold, or fuel air locks, fuel starvation. Tank vent, kinked pipes, that sort of thing.

There is further help in the link.

This is caused by minor cavitation. It is not an actual issue. What is happening is that your impeller is moving fast enough that it's drawing out the available supply of water since the boat is moving slowly and there isn't enough pressure on the bottom of the boat the keep the jet pump fed with the amount of water you're expelling out the nozzle. Water is fed into the tunnel in the transom by the pressure caused by forward motion at speed.

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