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Jet settings on '99 40hp

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  • Jet settings on '99 40hp

    Hi guys,

    I have a 40esrx, ('99 40hp). I replaced the top and bottom carbs. The main jets that came in the replaced carbs are 120. I can't tell what the old jets were (couldn't get them out - lead to replacement of carbs). The centre main jet is 118.

    I believe I need 115 jets in top and bottom, not 120. It's not running well when I rev it up - sputtering. It idles OK (idle jets 60 in all 3).

    It ran fine before I changed the carbs (I know - why did I mess with it then!), so I assume everything else is OK.

    Advice is appreciated.



  • #2
    Parts catalog and the SM call for number 115 main jets in the numbers 1 and 3 carburetors and a number 118 main jet in the number 2 carburetor.

    If the top and bottom carburetors have a number 120 jet I am not making a connection between that and the sputtering you are seeing. If the motor is propelling the boat at WOT that is.

    But since you need to do something, why not reinstall the original carburetors?
    Last edited by boscoe99; 05-23-2017, 04:03 PM.


    • #3
      are you positive they are 120 and not 130

      a 50 uses 130.

      where did these carbs come from?
      when I got my used C40 a previous owner drilled out the mains( I guess since the numbers were correct but holes where too big compared to new jets) that caused the motor to have a high speed miss.
      when I took the cowling and silencer off and ran into the wind it would run well, but not other wise.
      I replace the main jets and solved that problem.
      took me awhile to find the problem

      so too much fuel running threw a jet can cause a cylinder to miss fire,
      just not sure if a 120 would cause that
      Last edited by 99yam40; 05-23-2017, 06:59 PM.


      • #4
        I got it guys... Sorry, I'm a rookie here. I was revving the motor at the carbs, not at the remote. I'm embarrassed to admit!

        Thanks for the help.

        They are 120 jets, seem to run fine after I put it in the water. Except some starting issues...



        • #5
          where is this motor being run?
          sea level or on a lake maybe up in higher altitude?

          but I would think smaller jets would be needed in less O2 conditions

          the main thing is you have the wrong jets for some reason, so it is not fixed.
          I would need to look at all jets , even the air jets
          Last edited by 99yam40; 06-03-2017, 08:19 AM.


          • #6
            Where are the airjets?

            It's being run at se*****l.

            Should I replace the jet needles if I replace the jets? Meaning, are the jet needles for the 120 jets different than those of the 115?

            I'm not sure what the carbs came off of. I thought it was a 50hp around the same year, but it was last year and I can't recall...

            Thanks, Derek


            • #7
              look at a parts breakdown of the 40 and 50
              as I said the 50 lists 130 main jets and 62 low speed
              you can also look at the other parts to compare it to see if they are the same or different
              Last edited by 99yam40; 06-03-2017, 09:19 AM.