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  1. #1

    SLT780 Runs a Little Rough

    I have a 1996 SLT 780 that runs well from about half throttle to full throttle. The ski seems to run a little rough in the low RPMs but when it gets to about half throttle it has a sudden surge of power and takes off with a rapid increase in speed. This happens every time I accelerate from low speed and seems to happen at the same speed or throttle position. I have owned this ski about a month so I am not sure this is the way itís suppose to run or is something wrong.


  2. #2
    Polarisitis loonatik's Avatar
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    Good time to look at carb settings, clean or rebuild.

    Also, here's some good readings getting to know your ski, see link below:
    http://www.greenhulk.net/forums/showthread.php?t=148277

  3. #3
    Thanks, good information on the link you provided

  4. #4
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    This is normal.

    Well, the boost at a certain RPM is.

    If it runs rough below that there may be fuel issues. Depends on what you mean by rough.

    My driveshafts both make a fair amount of noise...and both my SLT780s have some exhaust noises at idle and when below the pipe.

  5. #5
    RLACEMAN's Avatar
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    You may be experiencing the power band of the 780 engine, they have a weak spot between 4200-4700, when driving at a faster speed, slowly let the rpms drop & when you get to around 4700, the rpms will usually drop to 3900 or so, then if you try to speed up gently there is a weak spot until upper 4K range & then the rpms jump very quickly. If you can hold the rpms steady at 5000 or above or 4000 or below this is normal if this is what you meant by 'rough'.

  6. #6
    ripcuda's Avatar
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    Quote Originally Posted by RLACEMAN View Post
    You may be experiencing the power band of the 780 engine, they have a weak spot between 4200-4700, when driving at a faster speed, slowly let the rpms drop & when you get to around 4700, the rpms will usually drop to 3900 or so, then if you try to speed up gently there is a weak spot until upper 4K range & then the rpms jump very quickly. If you can hold the rpms steady at 5000 or above or 4000 or below this is normal if this is what you meant by 'rough'.
    I've heard this described as "coming on the pipe"... a 2-stroke power-band thing. I too noticed this exact thing on my 780 I rebuilt... but not on my 750. Do you have this surge on the larger domestic engines?

    Cheers!

  7. #7
    BlueFishCrisis's Avatar
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    I get this on my 750.....

  8. #8
    RLACEMAN's Avatar
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    The 780 is the only ski I have noticed this on, I have driven every 2 stroke ski except a Hurricane & the 780 is the only one that does it, its not the pipe, as they are the same on the 750 & 780, the cylinder ports are higher on the 780 which causes this. Its like the old days when we ported the cylinders on snowmobile engines, we raised the exhaust ports to get more power, this moved the powerband a little higher rpm wise too, but at the expense of low end power. The 780 engine also has extra ports on the exhaust side which amplify this effect.

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