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  1. #1

    Join Date
    May 2006
    Okinawa Japan

    SC slippage or drivetrain?

    Hi folks,

    Noticed an ominous issue the other day...kept hearing and feeling a thumping/knocking sound in the hull.

    The first time I tried to check it out, I dropped the mrs and daughter on the nearest beach and switched to sport mode. Hammered the throttle and then the ski seemed to slip for a bit (not cavitation) then the slipping caught and the ski took off and ran normal after that through a series of accellerations from different speeds. Thought I may have had something caught in the pump (even though that wouldn't cause a physical knocking on the hull)...

    Put the family back on and continued on our way but kept hearing/feeling the thumping/knocking sound at mid RPMs. Wondered if it could be SC clutch slippage...

    Put the family back on the beach after a while and again put it through it's paces running it WOT and varying accelleration runs and again, could not repeat the problem.

    Stayed at that particular beach for a while and while on the way back home, noticed the problem showed itself in the 4500-5000 rpm range - repeatable. Faster or slower rpms, it seemed to disappear.

    Could not repeat the problem briefly trying to run it in that rpm range on the trailer while flushing

    Will check the pump bolts when I get home tonight. Can't see any reason for any drivetrain slippage other than those bolts but maybe I'm missing something.

    Also not sure of the clutch slippage problem symptoms...

    Any help of things to check before I take it back to the dealer would be greatly appreciated.

  2. #2
    mac_man_luke's Avatar
    Join Date
    Sep 2010
    South Australia
    Sounds like cavitation to me

    Increased load will increase cavitation as well

    Knocking could mean the prop is loose or maybe the pump

  3. #3

  4. #4
    knock/clunk/thud/thump is how I'd describe the same symptom in my sportster 215. Same rpm range too.

  5. #5

    Join Date
    May 2006
    Okinawa Japan
    Not cavitation - checked under the ski while it was in the water. Plus cavitation would be apparent when hammering the throttle from a dead stop. I had a loose prop on my STX-R once; totally different symptoms.

    Could be a broken motor mount but not easy to check for that on the RXTiS. Should not be a broken motor mount because I don't ride it hard in rough water but I haven't had a broken motor mount since my 95 XP days so it's possible that SD motor mounts break easier now than they did back then.

    I'll look into the pump/drivetrain more when I get home after work today...

  6. #6

    Join Date
    May 2006
    Okinawa Japan
    Checked the following tonight after work:

    Pump bolts: Everything tight

    Pulled intake grate and checked prop and shaft: no play

    Opened port side: bilge pump still attached where it's supposed to be. Water box looked a little out of place but to be honest, only had this side open once so it may be right. Strap is tight but I could still move the water box up and down - could be the source of the banging but doesn't seem likely.

    Checked engine mounts by trying to pull on the motor where I could get my hands in (RXTiS is damn tight to get into): Found an airbox support box loose. Could be the source of the knocking cause the air box is really close to the engine compartment cover. Did not find anything else and could not budge the motor like you can if a motor mount is broken.

    Checked the hull under the deck to see if something was caught in between the deck and the hull: Nothing there

    Checked the right storage side area: Everything tight except for the plastic sound suppression box. Seemed pretty loose to me with no tie down strap. Couldn't find a strap that would have/could have come undone so if one is supposed to be there, someone please let me know and post a pic if you can.

    Don't know what else to check other than putting it back in the water and riding it till it hard breaks...only got 22 hours on the ski so I hope I figure this out quickly...

    BTW - the mrs weighs all of 98 pounds and my daughter only 40 so adding them to the ski doesn't add a lot of weight to the hull. May make a difference on the suspension...if there is a problem with the suspension - no idea how to troubleshoot it.

    Jerry - is there a maintenance manual available for this ski?

    Chat again soon, cheers,


  7. #7
    Thought I'd update. Replaced my fuel filters and i no longer get the knocking at low rpms I described above. Picked up some rpm too!

  8. #8
    AtoMIC_OraNGE greenbullet's Avatar
    Join Date
    Jul 2010
    Barrie / BuckHORN Ontario
    could you be detonating? 4500-5k is when your creeping up on boost

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