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Yamaha engine - revving w/o thrust question

kwhalen

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New Yamaha 65 hp jet is revving high without thrust at >75% throttle, fully trimmed, no weeds in intake, ....feels like its "cavitating" like what happens on a prop boat. Any ideas?
 

Jebinok

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@kwhalen i suggest you ask this question in @HELP is this a jet ski or a boat? several possibilities: gutted coupling, slipping liner, we will need more info.
 

Bruce

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Most likely something is in the pump or the sealant is missing between the pump sections.

Being new, if you can not locate the problem perhaps take it to the dealer.
 

GTBRMC

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Hard to tell what boat you have, but if it is a Yamaha with a clean out port, check to insure the clean out plug(s) is/are installed in the port(s).
 

OrangeTJ

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I think he is talking about a Yamaha jet drive outboard. Sounds like cavitation so the place to start is in the pump housing itself - could be something as tiny as a piece of fishing line wrapped around the impeller or a piece of bark stuck between the impeller and the wear ring.
 

Geoff Cooper

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If you have checked for debris and the clean out ports are ok, Turn off the engine and with a long screwdriver fed from the gate check the impellor hasn't come loose it shouldn't turn, Failing that pull the pump out and check further can't be anything serious so don't get worrying, There's little to go wrong and it's a simple job you can do alone, There's loads of instructions on here if your not sure about pulling the pump out, Just shout, Get under the boat and check nothing is blocking the intake.
 

OrangeTJ

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Pretty sure he's talking about one of these, not one of the Yamaha boats.
103841
 

Geoff Cooper

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Oh i see, Sorry never worked on one of those but same principal it's not rocket science take your time and check, Input impellor output same as the jetboats you can still open the gate and see if the impellor is turning while it's out of the water again check for debris, That looks even easier to work on.
If that input is at the bottom as it looks like it is knowing the amount of water that it takes in and as it's well below the hull i would imagine in shallow water it's going to suck in some crap, I may shoot into town later this week and have a look see if they have one in, Interesting!!
 
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