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  1. #1
    DanSVHO's Avatar
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    Anyone experience this...

    Been driving me nuts and need to know if it’s normal. Upon getting on plane the ski feels like pump is not efficient and it revs but doesn’t accelerate as fast as you would expect given the amount of throttle input. There is a sensation of resonation, not vibration, as that is to harsh a word, at the rear end of ski. It feels like if I were to give full throttle from idle, something would break or burst. Like the pump tunnel. Of course, nothing ever does break but the sound and feeling tells you otherwise. It’s important to note, once on plane and the pump is loaded, I would say anything over 15-20, the ski reacts as expected with a given throttle input and the more throttle given you accelerate hard and normal. It’s always done this even before I resealed the transom. I was hoping that getting the transom resealed and modded would rid this but it has not. Is this a normal feeling? Is there a fix for this?


  2. #2
    Click avatar for tech links/info K447's Avatar
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    Year and model?

    Stock impeller?

    Stock intake grate?

  3. #3
    Hi SVHO,

    Only thing I can think of is a drone sound from the exhaust. I am assuming of course you have modded your Ski as I have seen your posts over the years. I have a Tommy Jordon exhaust mod and I get a drone and slight harmonics thru the back of the Ski at low speed\revs but once you get going with the wind in your ears then its all forgotten.


    Cheers


    Dave

  4. #4
    DanSVHO's Avatar
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    2019 Fx svho, modded grate, Solas prop13/16, extended Venturi smaller diameter, transom resealed.

  5. #5
    DanSVHO's Avatar
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    I suppose it can be that bit it still feels slower out of hole given a certain throtte
    input. If it felt the same as it did once in plane, then I would say it’s just resonation from exhaust and I would think about it. It’s the sound coupled with the performance at low speed that has me annoyed. Almost feels like there is seaweed in there and then it blows out once in plane.

    Quote Originally Posted by Spi200 View Post
    Hi SVHO,



    Only thing I can think of is a drone sound from the exhaust. I am assuming of course you have modded your Ski as I have seen your posts over the years. I have a Tommy Jordon exhaust mod and I get a drone and slight harmonics thru the back of the Ski at low speed\revs but once you get going with the wind in your ears then its all forgotten.


    Cheers


    Dave

  6. #6
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by DanSVHO View Post
    2019 Fx svho,

    modded grate ... transom resealed.
    I have GP1800 SVHO, not the new FX, so some of these comments are drawn from the GP1800 configuration.

    How well is the ride plate front edge sealed to transom plate bottom, the adjacent hull and to the intake grate bottom rear?

    Does the intake grate have a seal kit filling the casting voids?
    Is the rear face of the grate sealed to the transom plate?

    I am wondering if there is ventilation occurring until the hull speed is fast enough to change the hull water inlet from suction to pressure.

    At planing speeds the intake grate area has positive water pressure. At low speeds with throttle applied the intake has negative water pressure. Sealing leaks can allow air to be drawn into the water flow. The air would come from above the ride plate and leaks forward.

    Even a rather tiny air leak that ventilates the jet pump water intake flow can have a significant effect.

  7. #7
    DanSVHO's Avatar
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    I believe it is what you described. However i sealed it Better than what the factory did. I would’ve hoped this would’ve eliminated it. I wish somebody could give me a tutorial on exactly where to apply the sealant to ensure a tight seal. The back of a ride plate to the transom is sealed and the voids are filled on intake grate. Also, I retained the factory rubber fingers and molded them into the voids with casting resin. Other that that, I’m not sure what else to seal....
    Last edited by DanSVHO; 11-16-2020 at 04:26 PM.

  8. #8

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    Quote Originally Posted by DanSVHO View Post
    2019 Fx svho, modded grate, Solas prop13/16, extended Venturi smaller diameter, transom resealed.
    Sounds like pump pressure,pump efficiency on holeshot, iam assuming your using a 13/18 depitched to a 16 trailing with a smaller diameter nozzle, that combo would provide a healthy " on a roll" and top speed. Have you considered a lucky 13 with the stock nozzle bored out 2mm. This would also allow you to ditch the 13/16 for a 13/18 and tune the lucky accordingly for desired rpm. This is a much more favorable/ efficient setup and will produce results on holeshot,midrange pulls and top speed

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  10. #9
    DanSVHO's Avatar
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    yea, it’s a 13/18 de-pitched to a 13/16 to keep RPMs up given the extended smaller nozzle. Only problem is with L13 I would rid of the stock Bilge syphin.

    Quote Originally Posted by Yamafzs View Post
    Sounds like pump pressure,pump efficiency on holeshot, iam assuming your using a 13/18 depitched to a 16 trailing with a smaller diameter nozzle, that combo would provide a healthy " on a roll" and top speed. Have you considered a lucky 13 with the stock nozzle bored out 2mm. This would also allow you to ditch the 13/16 for a 13/18 and tune the lucky accordingly for desired rpm. This is a much more favorable/ efficient setup and will produce results on holeshot,midrange pulls and top speed

  11. #10
    I think you pretty much answered your own questions.A 16 degree pitch with a small nozzle is not moving as much water volume and can feel lazy on the bottom end.If you add a tail cone on that setup its just going to cork you up and you will be moving even less water.As mentioned in your previously thread a 18ish pitch and 85mm nozzle is usually the happy medium with the Yamahas


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