# Yamaha 40/30 Jet problem



## Charles munday (Jun 20, 2020)

Hey guys, I was wondering if anyone’s ever ran into this problem with a Yamaha 40/30 jet before. The Motor has been running great for some time now, just ran into this issue the other day. It cranks great and idles fine but when you go into full throttle the motor shakes violently and bogs down until I throttle back down. It’s mounted on a hog island skiff. Any help would be greatly appreciated, technicians seem to have little experience with jets in my area. Thanks! Here is the video of the issue


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## JC Designs (Apr 5, 2020)

Sounds like it’s cavitating and hitting the rev limiter. Check your impeller to liner clearance.

If you stay into the throttle, what happens?


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## Charles munday (Jun 20, 2020)

JC Designs said:


> Sounds like it’s cavitating and hitting the rev limiter. Check your impeller to liner clearance.
> 
> If you stay into the throttle, what happens?


thanks for the response! The motor just continues to violently shake and rev into higher rpms. So perhaps the motor isn’t mounted far enough below the bottom of the boar?


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## JC Designs (Apr 5, 2020)

Have you adjusted the height? In you initial post you say it’s ran fine until the other day.


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## Charles munday (Jun 20, 2020)

JC Designs said:


> Have you adjusted the height? In you initial post you say it’s ran fine until the other day.


I have never adjusted the height, I was just curious if that could cause it. I see now what you meant by checking the impeller to liner clearance. Thank you


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## JC Designs (Apr 5, 2020)

No problem! That clearance is pretty critical for proper operation.


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## Capt.Ron (Mar 5, 2014)

The impellers do wear down so you may have to shim it


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## Mcody31 (Jan 12, 2021)

Did you ever solve this issue? I do not have a jet foot but my Yamaha is doing the same exact thing after putting a new lower on it


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