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Thread: 175 Sport Jet Cavitating Problem

  1. #1

    Default 175 Sport Jet Cavitating Problem

    I've been spending a little time with AK Nimrod on the river and he is having a problem with his boat not getting on step. All the power is there, but it will just about kick up to jump on step then start cavitating badly and rev up the RPM's from 4100'ish to 6000+ and it will not jump on step. We pulled the boat and found that the front of the stomp grate had two bolts drop out which let it fall down about an inch and a half. A few hour round trip to Deadhorse to get two bolts later revealed that it wasn't the sole issue. We came closer to getting on step, but it had the same problem.

    He has torn it apart three times to clear it out and has not found any rocks or material in the jet unit. He replaced the sleeve and impeller before coming up here, so they are brand new. He is headed to Deadhorse later today because his wife goldstreaked up the old sleeve and impeller. Before he gets here, I was hoping to see if any of you guys had other suggestions on what it could be?

  2. #2
    Moderator bkmail's Avatar
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    Default Aknimrod

    Is the new impeller of the same pitch and blades...just a thought. Isuppose you'll know when the old one is compared to the one currently in the boat. It does sound like it is cavitating for some reason though.
    Good luck hunting and I hope you figure it out.
    BK

  3. #3

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    We got the old impellers and sleeves today. I'm back at work so I wasn't down there, but Nim called tonight and said that he put the old one back on and can get on step, it just takes a long time to do so. Sounds like the new impeller could be the issue, but he's back to the beat up one that limits his power. Guess he just needs to get on step and stay there.

  4. #4

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    Sounds like the new impeller is of too little pitch/diameter and is allowing the motor to over-rev. At this point at least, if the original fails completely, there is a back up to get him home faster than a dead drift at least.

  5. #5
    Member Roger45's Avatar
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    My hunting buddy and I spent some time with Nimrod on the Sag trying to help, watch what was going on. Terrible surging and what-not. This boat generally screams through the water so I was really surprised at how bad it was doing. He had put this *new and improved* housing an impeller on this summer and really had not tested it out before his 5 week trip up to the Sag. I am not convinced he doesn't have a fuel problem as well...maybe a little water in the gas??? He might try a little denatured alcohol or maybe some octane booster I sure hope he can figure this out before his son drives all the way up!
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    "...and then Jack chopped down the beanstock, adding murder and ecological vandalism to the theft, enticement and vandalism charges already mentioned, but he got away with it and lived happily ever after without so much as a guilty twinge about what he had done. Which proves that you can be excused just about anything if you're a hero, because no one asks the inconvenient questions." Terry Pratchett's The Hogfather

  6. #6

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    A surging issue sounds like a engine performance problem. I would start with fuel filters and isopropyl (red heet) , stay away from octane boost.

    Is this a 2stroke or 4 stroke ? Carb or FI ?

  7. #7
    Member chriso's Avatar
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    His son Rob is swinging by my house and pulling my hi-skew and housing off my boat to take up north with him as a back up plan. I cant help but think that new Solas impellor he tried may have something to do with his initial problems, and hope that his latest performance issues are simply due to his original impellor being due for a re-build. I know that when mine cavitates it surges almost exactly like Pat's been describing, so hopefully this solves the problem for him. I sure hate planning all year for your hunt and then spending the whole time mechanic-ing and troubleshooting, hope this works for them and gets them out in the field (and back!)

  8. #8
    Member Akgramps's Avatar
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    dont know if this will be helpfull?


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  9. #9

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    Jerod, this sounds somewhat similar to a problem that a friend of mine had. Look closely at the front edge of the jet intake, and see if it is possible that exhaust is escaping from there and getting sucked into the intake. With my friend's boat, this performance issue worsened with time, and was somewhat intermittent. He found that exhaust was getting out via a small gap around the jet intake, and causing massive cavitation problems at certain RPMs.

  10. #10
    Member Roger45's Avatar
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    Quote Originally Posted by 338WM View Post
    Is this a 2stroke or 4 stroke ? Carb or FI ?
    2 Stroke, Carb.
    "...and then Jack chopped down the beanstock, adding murder and ecological vandalism to the theft, enticement and vandalism charges already mentioned, but he got away with it and lived happily ever after without so much as a guilty twinge about what he had done. Which proves that you can be excused just about anything if you're a hero, because no one asks the inconvenient questions." Terry Pratchett's The Hogfather

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    Member Roger45's Avatar
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    Quote Originally Posted by longshanks View Post
    Look closely at the front edge of the jet intake, and see if it is possible that exhaust is escaping from there and getting sucked into the intake.
    This sounds promising. If you note the pictures I posted (behind Pump Station 2) the handy use of a Rhinhart 18 sided target as boat lift. He should have a great look at the bottom this way.
    "...and then Jack chopped down the beanstock, adding murder and ecological vandalism to the theft, enticement and vandalism charges already mentioned, but he got away with it and lived happily ever after without so much as a guilty twinge about what he had done. Which proves that you can be excused just about anything if you're a hero, because no one asks the inconvenient questions." Terry Pratchett's The Hogfather

  12. #12

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    It's not cavitating any longer after the old impeller was re-installed, so it isn't sucking the air like it was before. The performance is just way down now and it takes him a while to get on step. His son is bringing up some new parts, so hopefully he can get the pep put back in his step.

    Thanks for all your input. Nimrod called me today and I read him the responses.

  13. #13
    Member AK NIMROD's Avatar
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    thanx everyone for ideas,
    chriso thanx... parts my son got off your boat improved proformance to normal if not better. still not sure why boat did not proform well with new solas impellor and newly sleeved housing and then not back to normal as it was before new parts installed????
    home early ..son was in roll over accident (2-3 revellutions)on way home at toolik pass alive but cut and brused up.vehicle is totalled i'nm sure
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  14. #14

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    Pat, are you guys coming back up for moose hunting, or are you done up here for the season?

    Sorry to hear that the guys had a roll over. I'm guessing this is why you headed south early? Glad to hear they weren't hurt any worse than you mentioned, it sounds like they had a pretty bad wreck. If they end up shipping the truck down to Fairbanks and there is anything you need, let me know and I'll try to help out.

    Good seeing you again and congrats on your mini-bou!

  15. #15
    Member skybust's Avatar
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    ak nimrod

    glad to hear your son is ok.

  16. #16
    Member AK NIMROD's Avatar
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    thanx skybust
    Jerod, probaably done up north for this year would like to try for pike and maybe PWS deer and bear for a couple days
    RETIRED U.S.A.F. CAPT.; LIFETIME MEMBER NRA; LIFETIME MEMBER ALASKA BOWHUNTER ASSOC.
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  17. #17
    Member Crumm's Avatar
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    Quote Originally Posted by AK NIMROD View Post
    vehicle is totalled i'nm sure
    It sure looks like it is totaled. Glad to hear he is OK.

    I have heard in the past that Solas and Sporjet's don't go together real well.

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  19. #19
    Member AK NIMROD's Avatar
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    Crumm, solas seemed to work fine at first with the newly SS sleeved housing after 3-4 slides across gravel bar ( nothing out of the ordinary) it would not get on step would over rev. / cavitate at about 4k. i would figure i had sucked a rock drag it out of the water and check or even disassemble , small defects in leading edge of impellor filed and seemed to help a very small amount but again these defects were small and should not have been an issue.
    i think it is the adjustable plate below the nossle , tried adjusting it but was of no help.
    during the ongoing process when i realized the stomp grate was loose in the front and hanging down i thought for sure that was the problem really depressed when it changed nothing especially after driving to deadhorse 50 miles (40mph on washboard road) for bolts.
    RETIRED U.S.A.F. CAPT.; LIFETIME MEMBER NRA; LIFETIME MEMBER ALASKA BOWHUNTER ASSOC.
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  20. #20

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    AK Nimrod,

    this sounds like a problem my friend had. Not sure if you have done this yet or not, but closely inspect the front edge of your water intake for any hairline openings that exhaust gas can get out of. I posted this below, and I think it may be your problem. My friend dropped the grate, put some industrial sealant between the leading edge of the intake and hull, and his problem was solved.

    best of luck

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