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  1. #1

    96 slt 780 not reaching full rpms

    96 slt 780 only gets up to between 6150 and 6190 rpms, i think it hit 6200 once or twice on the water this weekend. On the trailer it will rev out all the way to 6750-6800. I have performed all the recommended upgrades and maintenance. Carbs are rebuilt and clean, new fuel lines all the way around, rebuilt fuel pump, has new boyeson pro series dual stage reeds in it. I'm wondering if maybe i have the high speed settings wrong, but not sure if it would be lean or rich that would cause it not to get all the rpms, also on the high speed screws mine have a plastic cap on them or something that limits their adjustability severely, do those just pop off? Any help will be greatly appreciated, thanks!


  2. #2
    BlueFishCrisis's Avatar
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    The 96 SLT 780 RPM top should be around 6400 +/- RPM. 6800 out of the water is hitting the rev limiter.

    The plastic caps do pop off of the high speed needles for adjustment purposes. You will need a small flat head screwdriver to adjust them after removal.

    You will want to look into your cylinders through the spark plug hole to see if you can identify piston wash. A rich running motor will show quite a bit of "clean" areas around the intake and exhaust port areas. A lean cylinder will be black all the way to the edge on the entire piston.

    In addition, binding in the splines or the jet pump bearings can reduce top RPM. Remove and check that your impeller is spinning freely and that the drive shaft splines appear to be in good condition.

    What spark plugs are you running?

  3. #3
    i am running the ngk bpr7es (the bpr8es seems to be impossible to find). Also will the reeds give it any more rev past the 6400 or should it still be right there?

  4. #4
    took the heads off and took pictures of the pistons, i know the pto is lean lean lean as it's solid black, the center i'm guessing is pretty lean as the clean spots aren't much and wondering if the mag cylinder is good or still a little lean, not a pro at reading piston wash so help and advice on how many turns off i am as a suggested starting point from where i am now would be great
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  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by jasonsmithftw View Post
    took the heads off and took pictures of the pistons

    ... the pto is ... solid black ...


    This piston has debris damage. Usually that means a crankcase bearing or piston pin bearing is coming apart.

  6. #6
    BlueFishCrisis's Avatar
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    Yup - Need to look into the PTO situation.

    Also, if the head gaskets are sitting the way they were oriented when you pulled the heads, they are not quite on right..... You should be able to read "78" and the shark fin should be under the water rail.... These heads have been off before as indicated by the copper gasket spray on the head gaskets.....

    Personally I would cal the CEN good, and the MAG a bit rich, but I'm no expert either...

  7. #7
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    Quote Originally Posted by K447 View Post
    Quote Originally Posted by jasonsmithftw View Post
    took the heads off and took pictures of the pistons

    ... the pto is ... solid black ...


    This piston has debris damage. Usually that means a crankcase bearing or piston pin bearing is coming apart.

    Yup. Thats not good.

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