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  1. #1

    Gp1800 pump stuffing

    So I finally got some smooth water this evening to do some test runs. The ski is running strong, I think I finally have most of the bugs worked out. But tonight while testing, the ski bucked at 76mph. Luckily it wasnít too violent and I wasnít thrown. I know a lot of you are running way faster than this with no issues. I have a few ideas why it could be happening but need some clarification on a few things.

    First off the pump Iím running is off of a 2015 fzs. So that would mean the exit nozzle has a diameter of 65mm, is that correct? When I get a chance Iíll measure and confirm. I thought I have read on here that the gpís come from the factory with an 87mm nozzle, is that correct?

    Iím running a Riva intake grate, 13/20 impeller, stock pump cone, and a modified Riva ride plate. Iím sure the 13/20 combined with the smaller nozzle isnít a good combo and the added angle on the ride plate probably isnít helping things either. So Iím thinking about opening up the nozzle to 87mm and see if that helps. I was also thinking about ordering a lucky 13 cone. How does the surface area of the lucky cone with no spacers compare to the stock cone? Does it have less surface area, i.e. create less pump loading. If thatís the case, Iíll definitely get one and experiment with the spacers and nozzle diameter.

  2. #2
    Also, what is the angle of the gp exit nozzle. I know the fz one I’m running is 3 degrees.

  3. #3
    GP OEM Exit Nozzle is 87mm @ 5 degree run the OEM Pump Setup and change the Impeller to 13/18 Pitch

  4. #4
    Ok, that’s what I figured I needed to do. Do you think the L13 cone would be worth getting as well?

  5. #5
    i test the Lucky 13 Pump cone on my stage 1 Plus GP two years ago.... it dropped the rpm down for around 350 rpm so you need to depitch the impeller to run the cone and then youīre able to dial in the rpm by the spacers... i run this setup on my stage 2 at the moment....i depitch the impeller to get the rpms back works perfekt

  6. #6
    Ok, that makes sense. Thanks for that information, exactly what I needed to know.


  7. #7
    I can’t think of a reason the pump would stuff at that speed without an issue with the intake grate.

  8. #8
    What should I be looking for in regards to the grate? I really wasn’t expecting to have this issue with this hull. Especially at only 76.

  9. #9
    I have seen people go as small as a 83mm nozzle with the new GP and that is not your issue.We run tunnel pressure gauges on all our skis and a few millimeters in nozzle size is not going to swing tunnel pressure drastically unless you are already close to the over stuffing threshold.I personally have never seen a Riva intake grate that did not eventually stuff at higher speeds.We tested one on a 95mph FX that was already running the R&D grate the other day and it stuffed the boat violently at only 40mph.I would remove the grate and try again

  10. #10
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    Quote Originally Posted by Mac800 View Post
    . . . . But tonight while testing, the ski bucked at 76mph. Luckily it wasn’t too violent and I wasn’t thrown.
    Equally glad for your safety, but is the context here singular, as-in bucked just once, or is this consistently occurring?

    I'm no expert by far, but I agree with the above comment in that your not exactly in the speed range for classic stuffing issues. Rather sounds to me like self-induced stuffing, possibly bumping against the RPM limiter perhaps - aka inducing a blip like of a throttle-chop scenario - IDK. Is there a tune on the ECU (RPMs), and do you know what the precise RPMs were leading up to the buck?

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