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  1. #1

    Difference in carbs?

    I have a 96 SL780, all 3 carbs are destroyed (don't ask, I have no idea). I came across a great deal ($16 shipped) on a set of good carbs from a 95 SL750. Is there enough difference in the jetting between these carbs to make a difference?


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Pass on the 750 carbs and get the 780 carbs that Frisco is selling in the classifieds.

    750 throttle cable is on the wrong side. It's set up for a single outlet fuel pump which means you will need to block off a couple fuel fittings on the carb rack. And the 780 carbs have better transition ports than the 750 carbs.

  3. #3
    No offense, but not what I asked. I know this info already. The carbs I got that are claimed to be from a 750 fit just fine, the choke and throttle cables are exactly the same. It is set up for a triple output fuel pump. The only difference is they do not have hook ups for the oil injection. But I don't really care. This is a budget minded ski, have right at $300 into it and want to keep it that way. It seems to be running fine with these carbs, lake test tomorrow will tell though.

  4. #4
    johnsonmtz's Avatar
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    Quote Originally Posted by X-Runner View Post
    The carbs I got that are claimed to be from a 750 fit just fine, the choke and throttle cables are exactly the same. It is set up for a triple output fuel pump. The only difference is they do not have hook ups for the oil injection. ....It seems to be running fine with these carbs, lake test tomorrow will tell though.
    Yes, they are both Mikuni SBN38 carbs. They can be made to work with some minor changes.

    1) Oil port. You are correct, the SBN38's on the 780 motors had nipples built in for the oil injection lines. The 750 versions did not and instead had fittings on the intake for the oil lines. If you choose to use these carbs you will need to either drill and tap the intake for fittings or block off the oil pump and go pre-mix.

    2) Jetting. Your SL780 calls for #67.5 low speed jets and #110 high speed jets. The 750's were spec'd out to have #75 lows and #90 high speed jets. In other words you will be running lean on the top end....which is bad.

    3) Pop-Off pressure. 750 carbs were set with the pop-off between 10-18PSI. 780's call for 22-24 PSI. You will be getting too much fuel on the low end causing the engine to load up in low speed conditions.

    Now, you could swap the jets from your 780 carbs into the 750's and install a new 2.0 needle and seat and set that to 22-24 PSI pop-off pressure. The high and low speed screws on your 780 should be set to 1 3/8 turns out on the lows and each cylinder like this:
    Mag - 1 1/8 turns
    CEN - 7/8 turns
    PTO - 1 1/4 turns

    If you do all this, you will most likely be okay.

    So, what I think Xlint was trying to say is that if you were to get Frisco's 780 carbs you would avoid all the swapping around and it would be a simple bolt-on install. The 750 carbs can be made to work, but it will take some effort.

    KJ

  5. #5
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    Last edited by X-Runner; 03-26-2011 at 09:31 PM.

  6. #6
    johnsonmtz's Avatar
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    That's too bad. The 780's are pretty durable motors. You would have to tear it down to find the real cause of the compression problems, but given your explanation of the carbs I'd say a good bet is the motor ran lean.

    Where are you located?

    KJ

  7. #7
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    Last edited by X-Runner; 03-26-2011 at 09:31 PM.

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Contact friscoboater. He's got a 780 engine for sale in the classifieds.

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