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Thread: Jet Performance Problems

  1. #1

    Default Jet Performance Problems

    Hope someone can point me in the right direction.

    I recently filed the leading edge of my impeller and replaced the wear ring. I did all this because the boat wasn't going as fast as I thought it should and maybe slow to get on step. I also moved shims around to get as close to the .03 possible. Its probably not as close as it should be but way closer than it was - 5 washers went up top.

    Anyhow, I just took it for a spin in the Knik and although I'm getting about 2-3mph (15% in my case) out of it better, it doesn't want to get on step very much (although it definitely does). Does anyone know what I could have done that would make it go faster but get on step slower?

    Confused by this. Maybe I filed the leading edge wrong?

  2. #2
    Member AKBassking's Avatar
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    Take a look at this thread. It gives some VERY good illistrations.

    http://forums.outdoorsdirectory.com/...ad.php?t=13717

    ALASKAN SEA-DUCTION
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  3. #3
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    are there groves in the impeller sleeve? if so I would replace it.

    my .02
    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  4. #4
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    Is this a new problem or something that has always existed in your boat/motor combo?
    How much does your boat weigh on the water and what size is your motor?
    These guys may offer some good advice to help you:
    http://www.riverjetmagazine.com/fuse...VIEWTMP=Linear
    Tennessee

  5. #5
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    Make certain you have the correct impeller. Some mid-range hp motors use a clipped impeller. Your problem may be that you aren't generating full rpm. Restricted rpm means you wouldn't be getting full power. Some motors won't spin a stainless impeller to full revs, either, even though the impeller is correct for that motor. It happens.

  6. #6

    Default Hmm

    The boat got on step just fine before I went and sharpened the impeller. I did follow the instructions in the other thread. After I sharpened it, it runs quite a bit faster wide open, just real slow to get on step. I took it all apart and reassembled it this afternoon. Maybe something wasn't attached right - we'll see tomorrow.

    What does the plastic collar/sleeve thing do? And what would it mean if there are grooves in it? Which there aren't by the way.

    Thanks for all the advice.

  7. #7
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    The plastic sleeve is a bushing that fits between the impeller and the shaft to eliminate metal-to-metal contact. I can't imagine how or why it would be "grooved".

    Always make sure there's no grass or rocks, even a little one, in the intake grate. Also look for any rocks n your outlet. Usually your impeller will cavitiate if the intake is restricted, but the rpm's and thrust will drop if there's any obstruction in the outlet.

  8. #8
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    opps... not the plastic sleeve. The cast one that fits inbetween the impeller and the foot.
    "When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
    Henry Ford

  9. #9

    Default

    I had a similar problem this weekend. The boat, no matter what I did, would not get on step. We pulled the boat onto a sand bar and checked the jet for sticks and to make sure everything functioned properly. We just couldn't figure it out. Everything looked fine. We ended up limping the boat back from just above the canyon to the copper river bridge. Once we put the boat on the trailer we pulled the foot. Everything, once again, looked great. Then I noticed the cable that controls the cup developed about 3/4" of play. The current was pushing the cup over the nozzle just enough to redirect some of the outlet water pressure.

    I thought I would give that a quick mention. It seems your symptoms are exactly the same as mine were.

  10. #10
    Moderator AKmud's Avatar
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    Quote Originally Posted by The Cleaner View Post
    I also moved shims around to get as close to the .03 possible. Its probably not as close as it should be but way closer than it was - 5 washers went up top.
    If you put the washers on TOP of the impeller, you went the wrong way. When all the washers are below the impeller and it is still out of adjustment, it is time for a new one. The object is to push the impeller up into the sleeve further to get the correct clearance.
    AKmud
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    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  11. #11
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    You've got it bass-ackwards. You put shims on top to tighten the tolerances as the impeller and sleeve wear. The cone is bigger on the top, so you're pushing the impeller deeper into the cone. When all the shims are on top, you're done.

  12. #12
    Moderator AKmud's Avatar
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    Default Duh....

    My bad, it was late last night when I posted that.... After 4 days on the Little Su (baking in the sunshine), I was a little fried!

    Pid is right, ignore my late night advice.

    As for sharpening, go here - impeller sharpening and look at the link for question #19. There is an image that explains how to sharpen the impeller.
    AKmud
    http://i78.photobucket.com/albums/j96/AKmud/213700RMK1-1.jpg


    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  13. #13

    Default We'll see

    Took it all apart and put it back together. Maybe something just wasn't lined up right. I'll take it out Thursday and see what it does. If that doesn't work, I'm going straight over to Professional Marine and buy a new impeller.

    This is an excellent forum, I appreciate all the advice and hope to be able to contribute here and there.

  14. #14
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    Another thing to consider is the trim setting on the motor, particularly if it doesn't have power trim. You need to play with the trim while the boat's loaded with your typical stuff. Unfortunately the out-of-the-hole performance and top speed usually don't both happen with one setting. You need to find your best compromise trim position and adjust the weight distribution to squeeze a little more performance when you need it.

  15. #15

    Default Back in business

    Thanks for all the advice.

    I ended taking it all apart and putting it back together, retuning from 35 to 40HP, and picking a pretty good sized rock out of the intake grate. It pops up on step real fast and hauls butt compared to before.

  16. #16
    Member AKBassking's Avatar
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    Amasing what a little rock can do to your jet!

    ALASKAN SEA-DUCTION
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    MMSI# 338131469
    Blog: http://alaskanseaduction.blogspot.com/

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