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VM Pilot Fuel Screws - Best Notch Setting

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    VM Pilot Fuel Screws - Best Notch Setting

    Hi All,

    Just finished rebuilding the airbox, carbs, replacing intake boot o-rings, adjusting points/static timing, and setting valve clearances. About to tune & sync the carbs.
    Bike is a 1979 GS750 with stock VM26SS carbs, stock air box, and stock mufflers. I am at 636 ft above sea level (fairly low elevation).
    Before I get started tuning, I would like my pilot fuel screws to be as close as possible to accurate as it may be some time before I can get to doing plug readings. Per the VM rebuild manual by Paul, if unknown, default adjustment should be ~1 turn. I tried counting turns but values were all over the place and I believe PO messed around with adjusting them. What I do have to reference, though, are the factory notches in the aluminum next to the screws. My thought was to select the setting that lined up with the notch and was closest to 1, but I'm not sure about the results. Below are the two values on either side of 1 turn out that would align with the notch in the carb - the value in bold is what I adjusted to - what do you think I should adjust to? Thank you in advance for your feedback here!

    Fuel screw adjustment (turns out)
    Carb 1: 5/8 or 1-1/8
    Carb 2: (aligns at 1 turn)
    Carb 3: 3/4 or 1-1/4
    Carb 4: 3/4 or 1-1/4
    1979 Suzuki GS750

    #2
    Forget the notches. Very lightly seat the screw, then back it out 3/4 - 7/8 of one turn. If you bottom the screw too tight, the tip will break off in the carb body. You've been warned.
    Ed

    To measure is to know.

    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

    Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

    KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

    Comment


      #3
      If you mean the front screw (next to the carb mount boot) than yes, start at 3/4 turn out and pretty much forget about it.
      The rear one, I run about 1.5 turns out. Still tweaking this as the engine starts to seat from the recent freshning up - complete top end.
      Not sure when the front screw was used because I have a set of '75 KZ900 - VM26's that don't have the front mixture screw.

      I have a 77 GS750 bored to a 844. However, I also have a Dyna ignition and 3 ohm coils, 4 into1 modified, factory air box heavily modified.
      However, this doesn't affect idle mixture much, I only need a little more and I've corrected most of this through pilot jet size. I'm running close to 16/16.5 - wire size drill bits

      Correct me if I'm wrong but I refer to these as:
      Rear - air metering screw - circle
      front - fuel mixture metering screw - arrow pointing to the area of the float bowl this is hidden in.

      image.png
      Current:
      1993 ZX11 - 2nd build in progress
      1977 GS750 (710 is getting closer)
      1998 Kawasaki Voyager - selling
      1998 Chevy C2500
      1999 Rav4

      Comment


        #4
        From a set of VM24's showing the front screw.
        These are from a 77 GS550
        Also, can anyone decipher the markings on the float bowl?

        Resized_20230708_144933.jpg
        Current:
        1993 ZX11 - 2nd build in progress
        1977 GS750 (710 is getting closer)
        1998 Kawasaki Voyager - selling
        1998 Chevy C2500
        1999 Rav4

        Comment


          #5
          Originally posted by unfocused View Post
          Also, can anyone decipher the markings on the float bowl?

          Resized_20230708_144933.jpg
          From what I can see, looks like maybe 30 ?
          1979 Suzuki GS750

          Comment


            #6
            Thanks for the advice. Looks like I'll be pulling the carbs, or at least the air box, to get to them & adjust - tried adjusting by shoving my hand in there with a flathead bit and I can't reliably tell how many turns out from seated I'm at. Oh well, that's what I get for overthinking it lol
            1979 Suzuki GS750

            Comment


              #7
              Originally posted by unfocused View Post
              From a set of VM24's showing the front screw.
              These are from a 77 GS550
              Also, can anyone decipher the markings on the float bowl?

              Resized_20230708_144933.jpg
              That's the pilot fuel screw
              the one on the side is the pilot air screw
              1978 GS 1000 (since new)
              1979 GS 1000 (The Fridge, superbike replica project)
              1978 GS 1000 (parts)
              1981 GS 850 (anyone want a project?)
              1981 GPZ 550 (backroad screamer)
              1970 450 Mk IIID (THUMP!)
              2007 DRz 400S
              1999 ATK 490ES
              1994 DR 350SES

              Comment

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