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  1. #1
    Trent_sl750's Avatar
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    Sl 750 piston wash questions.

    Took my ski out to do some plug chops to get it tuned right for the year and this is what my piston wash looks like, i dont know what it means.

    Did 5 short plug chops then back to trailer, plugs are brown, and before this pic the piston was to lean and completely black.
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  2. #2
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    Richen it up until you see fingernail sized clean spots near the intake ports.

  3. #3
    Trent_sl750's Avatar
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    The mag and cen have started the small spots on the edge but im near 3 turns out on my high speed screws on all of them.

    Do i need to upsize my main jet?

    if so what size do you suggest, and im not sure if they are the small or large jets?

    i plan on getting a air box off of a 780 motor.

  4. #4
    Trent_sl750's Avatar
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    This is what the other two look like. These pistons were all black on top and this is after 5 short plug chops and back to trailer with good plug color
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  5. #5
    BlueFishCrisis's Avatar
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    I'd say you're getting some water in there as well..... Stock jets are 90 main. You can get them for around $3 a piece. I would get a set of 95 and 100 so you have some options. You will save on shipping that way. You will want to go up on the mains with a 780 flame arrestor. I have a spare one here if you are interested - shoot me a PM....

    Did you perform a leak down test? If there are air leaks, the motor may still run lean....

    Make sure the head gaskets are installed correctly as well. The little "tab" goes under the water rail.

    Water intrusion will clean off the center / dome of the piston.... Use some copper gasket spray when re-installing or get a new set of gaskets if they are in bad shape. They are punched steel and will not work properly if reused too many times.....

  6. #6
    Trent_sl750's Avatar
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    I kind of figured there was a little water getting in there after checking it

    and yes i have done a leak down and it is 100% sealed.

    from what iv read, if your near 3 turns it needs to be up jetted, so you suggest get both and try them and see what best results.

  7. #7
    Trent_sl750's Avatar
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    So is it the small or large jets that i need, i see both options when i look and im not sure which i need for my 1995 sl750?

    thanks!

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