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  1. #1
    somefun's Avatar
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    Lost 200 RPM's Any Ideas???

    My DAM starboard motor is still only turning 7700. It's down 200 or so. I have no idea what it could be. I can't believe I have a boost leak with the HD high pressure clamps I have on it. I checked the intercooler, put in new spark plugs, Checked for WOT, Checked the SC clutch (75 inch pounds slip). It's got me baffled. Any Ideas? The other motor runs 7900 to 8000 all day. I even swapped the tac sender leads just to check and it was the same.


  2. #2
    SplishSplash's Avatar
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    Did you check your wear ring? Impeller nose cone? My ski ate a stick yesterday, got it out but RPMs were down 150 right away and its only minor damage to the wear ring.
    I was tirning 8050-8100 at 85F with 70% humidity.Ater the stick, cleared it and best I could get was 7900+-50
    How hot and humid was it?

  3. #3
    Water4fire's Avatar
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    Compression test it!!!

    .

  4. #4
    EZ Dock of Long Island Shibby1485's Avatar
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    at ANY given time, were the RPMs on both motors identical?

    i know there's an inherent thing with certain model yamaha jetboats that one engine runs less RPMs than the other bc of the hull design. one pump steals more water than the other, so they have aftermarket prop package with special pitches so RPMs are equal.

    just a thought

  5. #5
    somefun's Avatar
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    The motors did run the same at one time. I have checked the wear rings they are new SS Skat rings this year. The motors have about 70 hrs on them. The nose cone's looked fine. Not real sure on this one. The clamps I used on the IC are for high pressure applications. I really don't think they could be leaking. On the clamps that are on the aluminum tubes they are so tight that you can feel the tube flex as it gets tighter. But if it's not a boost leak then I have no idea. How do you know if its leaking? there is no way to see it or feel it with your hand? right? If I get a boost gauge the only thing is that the more the motor spins the more boost it makes so with the gauge in it and it down 200 rpms its going to show lower boost anyway...

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