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  1. #11

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    Quote Originally Posted by socalmxcool View Post
    please keep me up to date. I'm going to put the stock spacer on backwards since it still has a flat surface. I'm hoping that it will butt up against the R&D intake grate pump seal kit.
    I will. What spacer do you talk about?


  2. #12
    Quote Originally Posted by tomkve88 View Post
    I will. What spacer do you talk about?
    I cut off the knobs, so that side is uneven.

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  3. #13
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by socalmxcool View Post
    ... I'm going to put the stock spacer on backwards since it still has a flat surface.

    I'm hoping that it will butt up against the R&D intake grate pump seal kit.
    A new OEM seal would be optimal, but using the trimmed seal as it is I would suggest a bead of 3M 4200 Fast Cure sealant, applied along the entire front edge of the seal strip, before placing it into position.

    Fast Cure 4200 will take a couple of days to properly cure.

    You want zero air gaps, not even small ones, along the entire front edge of the ride plate and the hull and against the intake grate rear lower area.

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  5. #14

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    I done that last weekend, an used a good amount og sealent in those arreas you saying. But still having the cavitation from holeshot. I’ts mostly when raking a quick turn and then going out, it revs like it not have any water..
    not that bad for standing still, then I almost keep up with the org gp1800. I was thinking this eas solved by a new intake og impellar, but looks like socalmxcool still has the problem?...

  6. #15
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by tomkve88 View Post
    I done that last weekend, an used a good amount og sealent in those arreas you saying. But still having the cavitation from holeshot. I’ts mostly when raking a quick turn and then going out, it revs like it not have any water..
    not that bad for standing still, then I almost keep up with the org gp1800.

    I was thinking this eas solved by a new intake og impellar, but looks like socalmxcool still has the problem?...
    Multiple problem causes can have similar symptoms. If the cause is different then the fix may be different.

    If standing starts do not ventilate then your ride plate to intake grate sealing may be ok.

    Do you have a filler seal kit inside the cavities of the intake grate?

    Is the curve of intake grate upper rear edge properly sealed to the transom plate?

  7. #16
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by tomkve88 View Post
    I done that last weekend, an used a good amount og sealent in those arreas you saying. But still having the cavitation from holeshot. I’ts mostly when raking a quick turn and then going out, it revs like it not have any water..
    not that bad for standing still, then I almost keep up with the org gp1800.

    I was thinking this eas solved by a new intake og impellar, but looks like socalmxcool still has the problem?...
    Multiple problem causes can have similar symptoms. If the cause is different then the fix may be different.

    If standing starts do not ventilate then your ride plate to intake grate sealing may be ok.

    Do you have a filler seal kit inside the cavities of the intake grate?

    Is the curve of intake grate upper rear edge properly sealed to the transom plate?

    I am less familiar with how the FZ ride plate mates to the intake grate and the hull, as I have GP1800.

  8. #17

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    Quote Originally Posted by K447 View Post
    Multiple problem causes can have similar symptoms. If the cause is different then the fix may be different.

    If standing starts do not ventilate then your ride plate to intake grate sealing may be ok.

    Do you have a filler seal kit inside the cavities of the intake grate?

    Is the curve of intake grate upper rear edge properly sealed to the transom plate?

    I am less familiar with how the FZ ride plate mates to the intake grate and the hull, as I have GP1800.
    yeah off course.. I’m all agree with you on that.

    Standing starts not the biggest issue, most with quick turns and out.

    I have the pump seal kit fitting the org vxr grate, and orginal rubber sealant between plate and grate

    hmm... not sure I put so much sealant on the upper rear to the transom. But Worse now than original, and there was no sealent when tok it appart.

    some have good results with grate some with prop and some with filler seal inside the grate. But still havnet seen the best mod to do.

    like i mension earlier that i was thinking a new prop or grate would help me out. But just getting more confused by people having those mods still having cavitation.

  9. #18
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by tomkve88 View Post
    ... getting more confused by people having those mods still having cavitation.
    Cavitation and ventilation are different things. Different causes, different fixes. Some of the symptoms can be similar, but they are not the same thing.

    Lots of people will post about cavitation and then later on mention that better sealing of the jet pump area solved the problem. Better sealing will address air leaks into the jet pump intake water flow, which cause jet pump ventilation. So they had a ventilation problem but called it cavitation.

    Better pump and intake sealing will not fix cavitation. Cavitation is caused by the water getting ripped apart where it encounters the impeller blades or the fast moving water trips over an edge, such as the stator vanes or an uneven surface inside the jet pump.

    It is entirely possible to have both problems going on.

    Ventilation

    When accelerating hard from idle, the rapidly spinning jet pump impeller creates a strong suction through the water intake. There is negative pressure all the way from directly in front of the impeller blades to the hull area below the intake grate. The negative pressure draws the water upwards into the jet pump.

    If there are any places where air can leak into the water intake path then air bubbles will also be drawn into the impeller by the impeller suction. The jet pump is designed to process solid water. When air bubbles are present the impeller spins much more easily, but much less water pressure is delivered to the jet nozzle. Less pressure means less thrust.

    So the first symptom of pump ventilation is high revving at launch, yet thrust is diminished. Bigger air leaks equal less thrust, very small air leaks will have a more modest effect.

    As the hull begins to move across the water (accelerating rather slowly due to the weakened thrust) the forward motion starts to force water into the intake grate. As the hull speed continues to rise the water pressure in front of the impeller changes from a suction to pressurized water. Those ‘air leaks’ that were allowing air in are now spewing pressurized water out. Without suction the air bubbles don’t get into the water inlet flow - the impeller now has a properly solid water feed to work with and thrust quickly builds to the full expected power. Acceleration picks up.

    As long as the hull is moving with some speed, you can apply full engine power and get the expected thrust. Slow down too much and ventilation will be right back as soon as you get heavy on the power.


    Cavitation

    Unlike ventilation, cavitation can happen at any hull speed. Unless carefully guided and controlled, the tremendous amount of power being applied to the water by the impeller can literally tear the water apart. Localized ‘vacuum bubbles’ of low density water vapor occur with instantaneous violence. Cavitation bubbles can aggressively erode stainless steel surfaces and in extreme cases ‘burn’ the metal.

    Common causes of cavitation include damaged or rough edges on impeller blades (rock dings), rough edges on stator vanes, and discontinuous surfaces along the water flow path.

    With enough engine power it is also possible to induce cavitation in an otherwise perfectly good jet pump. The impeller just cannot maintain its ‘grip’ on the water.

    When cavitation occurs the jet pump thrust is reduced. Even at hull speeds fast enough to pressurize the water intake (making impeller ventilation impossible) heavy throttle application can still induce cavitation. At very fast hull speeds the incoming water pressure does help the impeller hang on to the power, but cavitation caused by rough edges will still occur.

    The fixes for cavitation depend on the causes. Damaged impeller blades need to be cleaned up, or replaced with a new or refurbished impeller. Rough stator vanes, same thing.

    If the impeller is simply inadequate for the available engine power then an aftermarket/upgraded impeller may be needed.

    The Yamaha 160mm SVHO jet pump has an unusual configuration. The actual jet pump body is 160mm inside diameter but the transom plate positioned directly in front is only 155mm diameter. So there is a 2.5mm right angle lip all the way round the circumference of the jet pump, right in front of the impeller. During high power this can cause the fast moving water to cavitate right before the impeller blades. Dean’s offers a modification service where the transom plate opening is enlarged to 160mm where it meets the jet pump, eliminating the edge.

    Cavitation can also be triggered by debris caught inside the jet pump. A rather small piece of wood can do it. I have had something as small as a plastic bottle cap create so much cavitation that there was almost zero forward thrust.


  10. #19
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by socalmxcool View Post
    2017 VXR with R&D performance kit (intake grate, Solas 13/19, air filter, reflash, sponsons) and riva ribbon delete mod. Took it out on Lake Mead and had a good amount of holeshot cavitation. Strong mid range ...

    Prop looks good, but the nozzle was off at a noticeable angle (noticed by a friend, I guess my time on my old Kawi 300 tainted my perception on that).

    So last year without the ribbon delete and intake grate it was 65mph with very little cavitation if any. . I'm pretty sure I did a poor job installing the intake grate / stock ride plate.

    ...
    Quote Originally Posted by tomkve88 View Post
    ...

    Standing starts not the biggest issue, most with quick turns and out.

    I have the pump seal kit fitting the org vxr grate, and orginal rubber sealant between plate and grate

    hmm... not sure I put so much sealant on the upper rear to the transom. But Worse now than original, and there was no sealant when tok it apart.

    some have good results with grate some with prop and some with filler seal inside the grate. But still haven't seen the best mod to do.

    like i mension earlier that i was thinking a new prop or grate would help me out. But just getting more confused by people having those mods still having cavitation.
    I would suggest a methodical approach.

    The jet pump can only work well if every thing is correct. It only takes one thing being not quite right to affect acceleration and/or top speed. In your case I suspect there may be several things that are not quite ‘perfect’.

    The jet pump nozzle(s) must be correctly aligned. Not sure what is going on there but you mention something being at an angle.

    The transom plate must be fully sealed to the hull. You might expect that the factory would do this well but it is not unusual for the factory sealant to not properly seal to the aluminum plate. My own GP1800 transom plate developed a couple of small gaps, which allowed so much ventilation that it could barely get up on plane. I removed the transom plate and resealed it much better. Acceleration problem went away.

    The intake grate has hollow casting cavities where it faces the transom plate. Filling the cavities with a seal kit (or DIY epoxy) eliminates one place for large air pockets to hide. But that is not enough. The entire perimeter of the intake grate rear face should be sealed to the transom plate. Some guys add a layer of sealant to the entire rear of the filler kit so that there are no voids at all anywhere behind the grate.

    A little sealant donut around each bolt hole before installing the intake grate is a good thing. Wipe away any excess sealant squeeze out.

    With the jet pump removed use an inspection mirror to check where the transom plate sealant meets the hull around the curved pump tunnel. And where the intake grate curved rear edge meets the transom plate. There should be a smooth sealant seal all the way around. No gaps.

    Make sure the transom plate 155mm hole is perfectly aligned with the molded hull curved tunnel opening. There are three alignment tabs molded into the hull to position the transom plate. If the plate is pressing against them then it should be fairly close to perfectly aligned.

    The bottom rear of the intake grate must seal to the ride plate front edge. This is the job of the factory rub seal strip. Put a strong work light on the floor right under the ride plate front edge, then look inside the top of the ride plate, around the front edges of the ride plate. You should not have any spots of light leaking through.

    On my own GP1800 I found the factory rubber sealing strip did not fully seal the ride plate to the hull. So I added a little 3M 4200 Fast Cure sealant where needed.

  11. #20

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    Quote Originally Posted by K447 View Post
    I would suggest a methodical approach.

    The jet pump can only work well if every thing is correct. It only takes one thing being not quite right to affect acceleration and/or top speed. In your case I suspect there may be several things that are not quite ‘perfect’.

    The jet pump nozzle(s) must be correctly aligned. Not sure what is going on there but you mention something being at an angle.

    The transom plate must be fully sealed to the hull. You might expect that the factory would do this well but it is not unusual for the factory sealant to not properly seal to the aluminum plate. My own GP1800 transom plate developed a couple of small gaps, which allowed so much ventilation that it could barely get up on plane. I removed the transom plate and resealed it much better. Acceleration problem went away.

    The intake grate has hollow casting cavities where it faces the transom plate. Filling the cavities with a seal kit (or DIY epoxy) eliminates one place for large air pockets to hide. But that is not enough. The entire perimeter of the intake grate rear face should be sealed to the transom plate. Some guys add a layer of sealant to the entire rear of the filler kit so that there are no voids at all anywhere behind the grate.

    A little sealant donut around each bolt hole before installing the intake grate is a good thing. Wipe away any excess sealant squeeze out.

    With the jet pump removed use an inspection mirror to check where the transom plate sealant meets the hull around the curved pump tunnel. And where the intake grate curved rear edge meets the transom plate. There should be a smooth sealant seal all the way around. No gaps.

    Make sure the transom plate 155mm hole is perfectly aligned with the molded hull curved tunnel opening. There are three alignment tabs molded into the hull to position the transom plate. If the plate is pressing against them then it should be fairly close to perfectly aligned.

    The bottom rear of the intake grate must seal to the ride plate front edge. This is the job of the factory rub seal strip. Put a strong work light on the floor right under the ride plate front edge, then look inside the top of the ride plate, around the front edges of the ride plate. You should not have any spots of light leaking through.

    On my own GP1800 I found the factory rubber sealing strip did not fully seal the ride plate to the hull. So I added a little 3M 4200 Fast Cure sealant where needed.
    thanks for much good info
    I will checj the things you are mension.

    Today it’s the national day of Norway, so today it wil hit be celebrating

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