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1993 Mariner 75 hp Carb idle setting - Which Way is Leaner?

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  • 1993 Mariner 75 hp Carb idle setting - Which Way is Leaner?

    I have a stupid question for everyone here. I have a 1993 Mariner 75 hp - three carb - motor. I have purchased a Factory service manual and have read all the sections of setting the idler jet screw. It states, initial setting 1.5 turns out, in water, in gear, warmed up, turn in each idler screw at idle until motor "Bogs or misfires", back out 1/4 Turn. Confirm with run. Do not run lean. Which way is leaner? In or out? I think in is richer, but nowhere in the factory service manual does it say..

    Please confirm....
    J Bisson
    ___________________________

    Current Boats
    1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
    1963 Sears 14' Utility - 9.9 Mercury (For Sale)

    Past Projects
    https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
    https://forums.iboats.com/showthread.php?t=457212

    Past Boats
    1991 Bayliner Trophy 2002 WA
    1971 Starcraft Chieftan 21
    1981 Lund Utility
    1961 Evinrude Tri-Hull

  • #2
    This the mixture screw or the one under sealed cap???
    When in doubt,Trim it out!!!
    Business Owner & Certifed Technician
    Boats I own & use
    20ft Javlin w/250 Junkrude
    17ft Bullet w/200 Merc (SOLD!!)
    13ft Allison w/150 I-6
    17ft Hydra-Sport 175GT
    15ft Allison w/75 Stinger(project)
    14 x 48 Drifter with 1100SS Merc

    Comment


    • #3
      no the one on top of the carp that the idle fuel mixture circuit is set by. Here;
      Click image for larger version

Name:	Idle screw.PNG
Views:	1
Size:	82.0 KB
ID:	10842517

      The reason I am asking, I rebuilt the carbs over the winter, had it out yesterday and set as per the service manual, and it was like 2 turns out when set accordingly. But when coming off plane the motor would cough and die on occasion if let down too fast. Ran great at full and mid throttle. and Idle without kicking too much.

      So this leads me to think that the idle circuit is too lean, but I don't know which way is leaner or richer.
      J Bisson
      ___________________________

      Current Boats
      1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
      1963 Sears 14' Utility - 9.9 Mercury (For Sale)

      Past Projects
      https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
      https://forums.iboats.com/showthread.php?t=457212

      Past Boats
      1991 Bayliner Trophy 2002 WA
      1971 Starcraft Chieftan 21
      1981 Lund Utility
      1961 Evinrude Tri-Hull

      Comment


      • #4
        Righty tighty lefty loosey. Could be too rich as well.

        Comment


        • #5
          Originally posted by DeepCMark58A View Post
          Righty tighty lefty loosey. Could be too rich as well.
          I know this, but if its an air screw, you get richer as the orifice gets smaller. If it is a Metering screw then the smaller the orifice, the less the fuel or leaner condition.

          So my question is is this an air screw or a metering screw. I looked at the carb the way it was built and I think this is a Metering screw. But want to confirm.
          J Bisson
          ___________________________

          Current Boats
          1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
          1963 Sears 14' Utility - 9.9 Mercury (For Sale)

          Past Projects
          https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
          https://forums.iboats.com/showthread.php?t=457212

          Past Boats
          1991 Bayliner Trophy 2002 WA
          1971 Starcraft Chieftan 21
          1981 Lund Utility
          1961 Evinrude Tri-Hull

          Comment


          • #6
            Ts a metering screw..in lean out rich
            When in doubt,Trim it out!!!
            Business Owner & Certifed Technician
            Boats I own & use
            20ft Javlin w/250 Junkrude
            17ft Bullet w/200 Merc (SOLD!!)
            13ft Allison w/150 I-6
            17ft Hydra-Sport 175GT
            15ft Allison w/75 Stinger(project)
            14 x 48 Drifter with 1100SS Merc

            Comment


            • #7
              Originally posted by Faztbullet View Post
              Ts a metering screw..in lean out rich
              Thank you.

              Another stupid question. I had reversed the enricher valve in and out. Would this have caused the issue of popping and dieing off plane? Sucking fuel thru the enricher valve?
              J Bisson
              ___________________________

              Current Boats
              1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
              1963 Sears 14' Utility - 9.9 Mercury (For Sale)

              Past Projects
              https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
              https://forums.iboats.com/showthread.php?t=457212

              Past Boats
              1991 Bayliner Trophy 2002 WA
              1971 Starcraft Chieftan 21
              1981 Lund Utility
              1961 Evinrude Tri-Hull

              Comment


              • #8
                Nope..its just a valve ..always closed until key activation.
                When in doubt,Trim it out!!!
                Business Owner & Certifed Technician
                Boats I own & use
                20ft Javlin w/250 Junkrude
                17ft Bullet w/200 Merc (SOLD!!)
                13ft Allison w/150 I-6
                17ft Hydra-Sport 175GT
                15ft Allison w/75 Stinger(project)
                14 x 48 Drifter with 1100SS Merc

                Comment


                • #9
                  Originally posted by Faztbullet View Post
                  Nope..its just a valve ..always closed until key activation.
                  Didn't know if it was a spring operated solenoid. and when pressure was back feed, that the valve would open allowing fuel to flow. Thanks for the response.

                  Also here is more to what I have going on. I pull the plugs last night. These where new before going for an hour total run time, 1/2-5/8 hour at WTO, and 15-20 at idle. Could not get it way down to idle on way back to dock or it would die cough and die out.

                  Click image for larger version  Name:	Plugs after first time out..JPG Views:	1 Size:	16.1 KB ID:	10842823

                  Can you tel me which one is leaner and which one is rich. From Left to Right is Bottom to top.
                  J Bisson
                  ___________________________

                  Current Boats
                  1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
                  1963 Sears 14' Utility - 9.9 Mercury (For Sale)

                  Past Projects
                  https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
                  https://forums.iboats.com/showthread.php?t=457212

                  Past Boats
                  1991 Bayliner Trophy 2002 WA
                  1971 Starcraft Chieftan 21
                  1981 Lund Utility
                  1961 Evinrude Tri-Hull

                  Comment


                  • #10
                    The one on the right looks like it is not firing.-------Simple tests to do.-------Compression test and post your numbers.----See if spark will jump a gap of 3/8" ( 1 cm ) on all 3 leads.----Is oil injection in service , tested or bypassed ?-----Water pump serviced ?-----Did your problems show up suddenly ?

                    Comment


                    • #11
                      Originally posted by racerone View Post
                      The one on the right looks like it is not firing.-------Simple tests to do.-------Compression test and post your numbers.----See if spark will jump a gap of 3/8" ( 1 cm ) on all 3 leads.----Is oil injection in service , tested or bypassed ?-----Water pump serviced ?-----Did your problems show up suddenly ?
                      Compression

                      125 PSI - Top
                      122.5 PSI - Mid
                      125 PSI - Bottom

                      All cylinders jump 7/16" Gap as per manual.
                      Carbs completely rebuilt, original jets, just new gaskets.
                      New water impeller kit
                      New Fuel Lines
                      New Plugs and gaped per factory service manual

                      One on right was wet. Other 2 where mildly wet with fuel, but have burn marks on them. I was thinking the from Right to left the mixture was richer, indicated by the dark marks....

                      Boat is a new acquisition to me. So not idea on the what was done prior to me other than the fuel pump being rebuilt 2 years ago.Seen dealer invoice for work and parts completed.
                      J Bisson
                      ___________________________

                      Current Boats
                      1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
                      1963 Sears 14' Utility - 9.9 Mercury (For Sale)

                      Past Projects
                      https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
                      https://forums.iboats.com/showthread.php?t=457212

                      Past Boats
                      1991 Bayliner Trophy 2002 WA
                      1971 Starcraft Chieftan 21
                      1981 Lund Utility
                      1961 Evinrude Tri-Hull

                      Comment


                      • #12
                        Take it back to the dealer I say.

                        Comment


                        • #13
                          Sign up today
                          Originally posted by racerone View Post
                          Take it back to the dealer I say.
                          Bought it privetly and it ain't going back!
                          J Bisson
                          ___________________________

                          Current Boats
                          1993 Lund Pro V 1775 Tiller - 75 hp Mariner & 4 hp Johnson Sail Master
                          1963 Sears 14' Utility - 9.9 Mercury (For Sale)

                          Past Projects
                          https://forums.iboats.com/showthread.php?t=521563https://forums.iboats.com/showthread.php?t=443915
                          https://forums.iboats.com/showthread.php?t=457212

                          Past Boats
                          1991 Bayliner Trophy 2002 WA
                          1971 Starcraft Chieftan 21
                          1981 Lund Utility
                          1961 Evinrude Tri-Hull

                          Comment

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