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  1. #1

    Mikuni SBN 38/40 questions on Low speed adj.

    So from what I read, the highs should be completely closed from the factory and the lows should be 1-1/4 out. I wanted to baseline what the lows were currently at since I have a wicked low end hesitation, most of the time it dies if I give it full throttle from idle while in the water. So while on the trailer I turned the lows in and they kept going and going, we are talking like 4 full turns in on the mag side carb. I started it up and it went up to 5000rpm. I quickly cut it and ran it out 1-1/4 turns. It still idled really high. I proceeded to turn them out until the idle went back down to 3k.

    Anyone have any ideas whats going on?


  2. #2
    Sounds to me like somone turned up the idle to make up for the overly rich LS needles. Set the needles to 1 1/4 again, back the idle down to 3000 on the trailer (out of water) then ride it. That will give you a starting point.

  3. #3
    Quote Originally Posted by Piranha Performance View Post
    Sounds to me like somone turned up the idle to make up for the overly rich LS needles. Set the needles to 1 1/4 again, back the idle down to 3000 on the trailer (out of water) then ride it. That will give you a starting point.

    Thanks for the advice. Question for you though. I turned them in until the screwdriver got stiffer, I could still turn them in further but decided against it not knowing how strong the threads are. And to be certain that I'm adjusting the correct ones, they are on the bottom of the carbs and actually have a bar going through them unlike the High speed adjusters that are covered with plastic caps on the top correct?

  4. #4
    Correct. Make sure they are snug before starting to back them out 1 1/4.

  5. #5
    Do you know where the idle adj is? And if its separate for each carb?

  6. #6
    It is near the fuel line inlet towards the front. Its a T handle like the LS adjusters. It is for both carbs.

  7. #7
    Thanks again.

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