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Thread: rpm loss??

  1. #1
    bradsta's Avatar
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    rpm loss??

    Hi all, took my 08rxpx for a river run today all was going well, ran a best of 78.4! (mods listed below) but noticed on the way back i was starting to drop revs.
    Ski was turning 8440rpm (8650 reflash) with good speed on the way up the river, but on the way back went from 8440 down to 8300 then down to 8220 then 8100 and finished at 8020rpm?
    The run was for about 10-15min flatout eachway, up and down the river, so i know the motor was working hard and will be getting hot and loose rpm but does the problem i had sound like a heat issue or s/c slipping maybe? Or am i just stressing?? Ski has a sdc thermostat fitted and had the s/c rebuilt 10hrs ago??
    cheers bradsta..


  2. #2
    Moderator Snoman's Avatar
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    i would start by checking/resetting the Scer slip...

  3. #3
    ou812's Avatar
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    Make sure the SC wheel itself isn't spinning on the shaft. I chased my tail for months replacing schit & cursing even rebuilt the motor. Then I rebuilt the 2rude & today it ran perfect.. Thanks to Seadoo1120's help, I found that the Wheel was spun on the shaft & would cause havoc on my AFR,rpm, etc.... Gained my 500+ rpm back & all power too.

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    monaroman76's Avatar
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    Quote Originally Posted by bradsta View Post
    Hi all, took my 08rxpx for a river run today all was going well, ran a best of 78.4! (mods listed below) but noticed on the way back i was starting to drop revs.
    Ski was turning 8440rpm (8650 reflash) with good speed on the way up the river, but on the way back went from 8440 down to 8300 then down to 8220 then 8100 and finished at 8020rpm?
    The run was for about 10-15min flatout eachway, up and down the river, so i know the motor was working hard and will be getting hot and loose rpm but does the problem i had sound like a heat issue or s/c slipping maybe? Or am i just stressing?? Ski has a sdc thermostat fitted and had the s/c rebuilt 10hrs ago??
    cheers bradsta..
    Hey Bradsta, when my ski was running that charger I saw very similar rpms with the 15/22r. As Scott says, start by checking the supercharger slip - That could certainly be your issue.

    As you mentioned, heat fade will cause some loss of rpms, but I think 400 or so is a little much. Possibly check for an exhaust leak into the hull?? What were your afrs?

  5. #5
    Having Fun jp1300r's Avatar
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    You need to check slip a few times after a rebuild especially with the new OEM black washers. Maybe every two hours of running 2-3 times. Do you know your AFRs? Check compression.

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    bradsta's Avatar
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    Thanks guys, jp the charger was rebuilt with oem kit and washers, no shims.
    As for AFR's i don't monitor them as yet. When the ecu was done at sdc, they assured me i would be good for fueling??
    Will check slip on charger first. When checking the slip i just need to by the s/c holding plate and the shaft holding tool yeah? I have a torque wrench already, so is that all i need (aswell as mcmaster washers and shims)??
    cheers bradsta..

  7. #7
    monaroman76's Avatar
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    You do not need to remove the s/c to check the slip. Lock the cam or stick something in the prop to stop it from turning. Then you can check the slip by turning the impeller but counterclockwise (as to not loosen the nut) and your done.

    If your going to remove it the check, it's the gear holder tool you will need, not the shaft holder tool. However you will need the shaft holder tool if your are going to be disassembling it to shim/ replace spring washers.

    Good luck.

  8. #8
    bradsta's Avatar
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    M76, i'm good with tools but shimming the s/c just seems a little daunting!!
    Is it pretty easy to do?, just the thought of fooking it up and toasting the motor makes me paranoid!!!
    And it's more accurate to check the slip out of the ski yeah??
    thanks bro!
    bradsta
    Quote Originally Posted by monaroman76 View Post
    You do not need to remove the s/c to check the slip. Lock the cam or stick something in the prop to stop it from turning. Then you can check the slip by turning the impeller but counterclockwise (as to not loosen the nut) and your done.

    If your going to remove it the check, it's the gear holder tool you will need, not the shaft holder tool. However you will need the shaft holder tool if your are going to be disassembling it to shim/ replace spring washers.

    Good luck.

  9. #9
    monaroman76's Avatar
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    Quote Originally Posted by bradsta View Post
    M76, i'm good with tools but shimming the s/c just seems a little daunting!!
    Is it pretty easy to do?, just the thought of fooking it up and toasting the motor makes me paranoid!!!
    And it's more accurate to check the slip out of the ski yeah??
    thanks bro!
    bradsta
    Don't be nervous about it at all. It's pretty hard to go wrong. It's installation of bearings that is crucial and if done incorrectly can cause big issues. The clutch assembly is pretty straight forward. As long as you keep things very clean, apply engine oil to parts before installing and torque the back nut up correctly (22ft/lbs) with loctite, you will be fine.

    It wont matter if you check the slip with the s/c installed or on the bench - You should get the same readings provided you have the engine locked.

    Are you using a dial type wrench?

  10. #10
    bradsta's Avatar
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    Yeah mate, using a 1/2" dial torque wrench.
    So when checking slip it's only spring washers and shims and adjustment of l-collar isn't it?
    The charger was freshly built 10hrs ago, so i shouldn't need to go touching bearings correct??
    Read jerry's "how to shimming s/c" thread, over and over so hopefully ready to give it a go!!!!

    bradsta..

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