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Thread: Low RPM Issue

  1. #1
    xenonx's Avatar
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    Low RPM Issue

    Need help diagnosing...

    05 RXT with 8 hours.
    With Riva Stg II I was running 7900rpm at 2200 elevation.
    Boat ran strong with no issues when previously ran.

    Ran at same lake and could only get to 7350rpm and then dropped to 7250rpm max. Checked engine temp etc. and all was good. Checked to see if I sucked anything into pump and all ok...prop ok...wear ring ok.
    Pulls ok out of the hole but will not rev out like it used to the previous ride. I did not change anything from the previous ride except fill ride plate holes and match grate to hull. At the lake, I pulled the intake hose off to check SC impeller and could not slip by hand. Checked plugs and all OK visually. Oil level ok. Ran 1 tank of gas through and nothing changed excpet for slight loss in rpm which was probably heat soak as I have not installed the thermostat yet.

    Took to dealer and checked on computer. The only thing that came up was throttle position sensor slightly off. We checked throttle stop and reset sensor on computer. We also checked to make sure knock sensor was plugged in good as well...ok.

    Would the TPS sensor be enough to make me drop 500-700rpm? It was not off by much. Maybe 1-2% tops. Definitely seems to be engine related vs. prop-pump issue. Maybe bad plugs although they tested ok on the computer. Will replace anyway to make sure not bad under load. Will reseal IC plug although I sealed well when installed not long ago. Have heard of issues with slipping SC but at 8 hours?

    Anyone have any ideas as to what might be the issue?
    HELP!


  2. #2
    Top banana's Avatar
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    Sound like clutch to me slipping abit get the dealer to check the slip ?

  3. #3
    xenonx's Avatar
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    Quote Originally Posted by Top banana
    Sound like clutch to me slipping abit get the dealer to check the slip ?
    OK...but with only 8 hours of fairly smooth water riding?

    Have others lost this much rpm with slipping clutches?
    Those that have experienced slipping clutches please chime in.

  4. #4
    Top banana's Avatar
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    05 have a major probiem with clutches

  5. #5
    Yeah, do something simple first and change out the plugs, if they or you hadn`t done so for the season already. If the engine was fogged properly, you could have fouled plug or plugs...PR...

  6. #6
    xenonx's Avatar
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    Low RPM Issue

    Quote Originally Posted by Pale Rider
    Yeah, do something simple first and change out the plugs, if they or you hadn`t done so for the season already. If the engine was fogged properly, you could have fouled plug or plugs...PR...
    PR, I checked all of the plugs at the lake. All looked good but you never know. I changed out the rear as it looked to have slightly more deposits on the electrode. Changed the plug and no difference. Will change all to new anyway. Checked oil and it looked ok..no deposits or such.

    I will check the clutch but mechanic says he doubts it is the clutch. Says he has never seen an 05 with a clutch problem....he works on plenty of them here in Southen Ca. If it is a slipping clutch at least I will have diagnosed the problem and go with the metal clutch washers...should probably order a set now anyway.

    Again, those that have had slipping clutches, did you experience a drop of 500-700 RPM?

  7. #7
    EZ Dock of Long Island Shibby1485's Avatar
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    having a boost gauge would be a nice item to really eliminate a boost leak. you'll really never know without a gauge.

    a slipping clutch varies on how many RPMs u lose.... if u totally lose the supercharger, it's almost always 6800 rpms that you will see...

    so your TPS was off... that could contribute a bit, yes.

    you have two options in my opinion.... take it in and have a slip test performed before you put it in the water.... OR... put it in the water now that the TPS is reset and see if it does the same thing.. if still missing alot of RPMs, dont ride it anymore, take it in and get the SC looked at so u dont wind up with worse damage and bad downtime.

  8. #8
    xenonx's Avatar
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    Steve,

    I agree, I need a boost guage immediately...especially since I have more mods planned after I get past 10 hours.

    I am going to probably throw in the metal clutch washers regardless of how the clutch specs out. I want to rule slipping out once and for all and not deal with the ceramics.

  9. #9

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    Low RPM issue

    Reseal the IC block off plate. Use plenty of silicone. Check the IC tubes. Do not overtighten. I really do think it's a boost leak. Are you running at pyramid?

  10. #10
    xenonx's Avatar
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    Curt,

    I did seal the blockoff very well, however, I will re-check.
    The RXT is in the shop under warranty and I trust we will get it sorted out. I hope it is a slipping clutch and get it replaced with the new assembly. When Jerry gets the metal clutch washers in, those will be next.

    Yes, I have been riding at Pyramid lately as I cannot stand Castaic.
    My friends and I take off work on Thursdays when we can to ride as the weekends are too crowded.

    Met John Annick last week. Very nice guy. He invited us to go on a ride to Catalina as he and others are practicing for the Catalina race.

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