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Pilot air screw size question

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    #1

    Pilot air screw size question

    1981 GS850G

    2 parter

    1. What part of the circuit does the PILOT AIR JET (the wee one in the intake throat of the carb) play & affect the most? From the diagram of the carbs, it seems to add a fixed amount of air direct to the idle circuit. Does it have any effect as the throttle is opened up? Does it add MORE air as the number gets higher?

    2. Depending where I look (from Suzuki's printed specs to the Haynes manual to several specs in posts & charts here in GS Resources)
    I find either 180, 190 or 200. Then it seems the GZ dropped back to 180.

    My bike, from when I got it in 2002 or so had 180 jets. Suzuki specs said 190, so I changed to 190s. Now I see some references to 200 size.

    Thanks,

    DH
    Tags: None
    #2
    The pilot air jet effects mostly midrange power but also contributes all the way to wide open throttle to some extent. The changes in pilot air jet sizes coincides with changes in the pilot jet and needle changes. Seem that Suzuki did a little experimentation over the course of 3 years with the CV carbs. Also seems that the 180 pilot jet and 40 pilot fuel jet was the happy medium. For what it's worth the needle jet was also changed but when ever the 180/40 combination was used, so was the 5D50 needle. All of the combination worked so I'd use what you have now and go with it. If you would like to go to the 180/40/5D50 combination then let me know and I can provide you with that combination. For what it's worth, the main air and main fuel jets stayed the same over the same three year period.

    1980 GS1000GT (Daily rider with a 1983 1100G engine)
    1998 Honda ST1100 (Daily long distance rider)
    1982 GS850GLZ (Daily rider when the weather is crap)

    Darn, with so many daily riders it's hard to decide which one to jump on next.

    JTGS850GL aka Julius

    GS Resource Greetings

    Comment

      #3
      If your idle became loopy put the other jet back in.
      This air jet uses the air that is pulled into the engine to suck fuel from the main jet which is blocked by the jet needle. It is diverted to the pilot jet and is introduced to the engine through a port in the venturi.
      The idle mixture screw determines how much air and fuel mixture is introduced. The pilot air jet controls the amount of air in this mixture and the pilot jet size determines the fuel.
      Since the needle has not risen out of the main jet this circuit is used mostly for idle and off throttle. They all work in combination and you want a smooth transaction between each circuit.
      1 pilot circuit
      2 needle circuit
      3 main circuit
      1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
      1985 GS1150ES stock with 85 Red E bodywork.

      Comment

        #4
        Yep, chef is right. Was thinking needle circuit and talking pilot. Teaches me not to post when I'm tired. Sorry for any confusion.

        1980 GS1000GT (Daily rider with a 1983 1100G engine)
        1998 Honda ST1100 (Daily long distance rider)
        1982 GS850GLZ (Daily rider when the weather is crap)

        Darn, with so many daily riders it's hard to decide which one to jump on next.

        JTGS850GL aka Julius

        GS Resource Greetings

        Comment

          #5
          Originally posted by chef1366 View Post
          If your idle became loopy put the other jet back in.
          This air jet uses the air that is pulled into the engine to suck fuel from the main jet which is blocked by the jet needle. It is diverted to the pilot jet and is introduced to the engine through a port in the venturi.
          The idle mixture screw determines how much air and fuel mixture is introduced. The pilot air jet controls the amount of air in this mixture and the pilot jet size determines the fuel.
          Since the needle has not risen out of the main jet this circuit is used mostly for idle and off throttle. They all work in combination and you want a smooth transaction between each circuit.
          1 pilot circuit
          2 needle circuit
          3 main circuit
          Thanks chef1366. I didn't think it was that critical as when I found the 180 & installed the 190 per Suzuki's parts listing, I didn't notice any difference at all.

          Funny about the post of all the twiddling of jet combos. Reminds me of my early days riding JAWAs. The Czechs would make design & production changes mid week & never mention it so all the parts books were suspect. We had an old Czech guy who came over from the factory at American Jawa on Long Island. I think he had every part number & all the cross references memorized & would laugh at us when we referred to a book. I think he had a secret radio connection to an insider at the factory so he'd be up on all these changes.
          Over here we are really stuck on exactitude & get antsy when there are undocumented variations. You never know though when that is important or not until you break down in Podunk on a rainy Sunday night with a dead cell phone.

          Thanks again for the enlightenment. I won't be changing any over, I do have the #40 Pilot & believe the needle is the one mentioned as well.

          DH

          Comment

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