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  1. #1
    PWD Filoo's Avatar
    Join Date
    Jun 2007
    Charleston, SC

    Stable engine speed.. How stable?

    What's a reasonable amount of + and - rpms when the engine (150 Speedster SCIC 2007) is running at slow speed?

    Everything runs smoothly above 4,000 rpm. But when I idle along, say around 2,760 rpm, it actually tends to flutter randomly between 2,700 and 2,820 rpm. You can also tell that it's not a steady sound, you can hear it revving up & down...

    I've only noticed fluctuations of up to +/- 60 rpm, is this normal? I expected 4 strokes to have a more regular rotation speed...

    PS: the water is not choppy but pretty glassy without currents, so that's not the reason. Is there a way to fine tune the idle setting to a more stable regular speed?
    PS2: Could be the propulsion rather than the engine, but I have not tried running it out of the water at those rpms to rule out a problem with the impeller. Is it safe to do?
    Last edited by Filoo; 07-26-2007 at 07:01 PM.

  2. #2

    Join Date
    May 2007
    Mine does the same thing at lower RPMs (idle up to about 2800 give or take) I just think it is the normal actions of the motor. Not knowing what the torque band is on our motor it could be (I am not an engine guy, so don't quote me) the engine trying to maintain the RPM by constantly adjusting the fuel flow, but not keeping up with itself. Maybe some one with more insight could enlighten us both.


  3. #3
    PWD Filoo's Avatar
    Join Date
    Jun 2007
    Charleston, SC
    I wonder if this only happens with jetboats or also with skis...


  4. #4
    King_Of_Fun's Avatar
    Join Date
    Jul 2007
    Catawba Island, Ohio
    My 185-hp SC does the same thing. I think it's the ECU changing fuel mixtures/rpms to maintain low emissions levels.

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