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  1. #1

    How to identify different Mikuni carbs on SL780

    I noted the SL 780 can have either one of two carbs, the one "with first transition holes above throttle plate" and the other below. With the carbs removed, I can see 4 pin holes in the throat of which 3 are above the plate at idle and one below - I assume these must be the transition holes ? Can anyone confirm this please ? I am new to this, but learning.

    My ski stops firing on one cylinder above 3500 rpm, as if it starves of fuel. The carbs seem to have been set for the transition holes below the throttle plate and in that case it is running lean. (eg Above Mag cylinder = 1 1/8 turn, below = 3/4 turn).


  2. #2
    were did u read that? thats interesting! you won't hurt anything by fatting it up! but if it is indeed leaning out you better find the reason quickly! Z

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    If it hasn't been done recently, I'd rebuild the carbs and change the fuel hoses. Check your fuel filter, fuel selector valve, and water seperator for blockage.

  4. #4
    cheatin' piston popper addicted's Avatar
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    I know that there are 2 different jetting specs for them. I saw it in my manual. Unfortunately it is at the lake and I am not. I'm sure someone else has the factory book and can look it up for you.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by addicted View Post
    I know that there are 2 different jetting specs for them. I saw it in my manual. Unfortunately it is at the lake and I am not. I'm sure someone else has the factory book and can look it up for you.
    He'd be right about that. What year are you looking at? 95 differs from 96. 96 has 2 different settings for 780s. And 97 differs from both 96 settings.

  6. #6

    Smile Model and info

    Thanks for the replies, its a 96 model 780. The Clymer manual mentions the two types of carbs, but only distinguishes by the description of the transition holes above or below, no picture or photo. That is what I am trying to confirm.

    The ski was built up by someone and sold by a local boat dealer who will not give me info on the builder. I have my doubts about his knowledge as the oil pump linkage was assembled wrong already, just want to be safe and not cook the pistons or cylinders running too lean.
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  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Well you can always play it safe and go with the fattest settings. Check your piston wash, and start leaning them out if it's too rich. OR check the serial number on the block. My book shows a number EC78PWE-02/05 for SL 780. EC78PWE-03/04 for a SLT and EC78PWE-04 for the SLX 780. The SLT and SLX adjustments are the same

  8. #8
    ph2ocraft's Avatar
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    Carburetors used on 03/04 have the 3 transition (by-pass holes) all three above the butterfly.
    main jet is 110
    pilot jet is 67.5
    High Screws
    Mag=11/8 turn
    Cen=7/8
    PTO=11/4
    LowScrew is 13/8 turn

    Carburetors used on2/05 have 4 transition (by-pass) holes 3 above and one below the butterfly.
    main jet is 107.5
    pilot jet is 72.5
    High Screws
    Mag=3/4
    Cen=3/4
    PTO=1
    Low Screw is 5/8 turn

    Remember if you're using fuse with ethanol of at least 10% open the high speed screws an extra 1/8 turn.

  9. #9
    Connecticut CrazyA's Avatar
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    Nice Al I have that somewhere, but for the life of me couldn't find it!!!


    .

  10. #10
    ph2ocraft's Avatar
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    Quote Originally Posted by martinv View Post
    My ski stops firing on one cylinder above 3500 rpm, as if it starves of fuel. The carbs seem to have been set for the transition holes below the throttle plate and in that case it is running lean. (eg Above Mag cylinder = 1 1/8 turn, below = 3/4 turn).
    So, with the jetting correct, my guess is you have an ignition failure?
    Any flashing lamps on the MFD?
    Have you cut the plug wire ends about 1/8-1/4 inch so the spark plug end (resisitor 5K ohms) twists into some fresh wire?
    What makes you think it's fuel related vs. electrical?
    Back to the carbs, is the fuel fresh?
    Any excessive trash in the tank?
    Hoses bent over?
    Take on any water into the hull lately?
    Compression is good?
    Crank Index good?
    Spark plugs new, with the correct gap?
    Anyway, some thoughts.

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