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What is 'extra' port on carb body/float bowl flange? Matching hole in gasket not bowl

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    #1

    What is 'extra' port on carb body/float bowl flange? Matching hole in gasket not bowl

    So I'm re-assembling a set of BS34SS carbs off a recently-acquired 1981 GS1100E. It's my first time rebuilding this particular model of carbs, but have done similar work on cars and other bikes over the years. There are several useful photoguides and videos on this website and elsewhere that have guided me through the specifics pretty well so far. However during final re-assembly I went to go install the float bowls and noticed something odd. There is a hole/port on the carb body, located on the float bowl gasket flange ('behind' and slightly to the side of one of the float pivot pedestals). There is a corresponding hole in the gaskets to matches up with this hole, however, there is no corresponding hole in the float bowl itself, and if the float bowl is installed, you can see that the hole/port in question seems to be open to atmosphere. And based on how the gasket forms around it, I suspect it is meant to be sealed somehow, or connected to some port inside the float bowl? Looking at all the photo guides and such, none of the carbs in them have this hole, though the gaskets used all have the corresponding cutout in them (it just appears unused on the carbs featured in the rebuild guides). I have attached a picture showing the hole in the carb body (circled), with the gasket laid atop, and then with the float bowl mounted (showing that the bowl doesnt cover the hole or gasket completely and it is open to atmosphere).

    Mystery carb port.jpg

    So questions:
    1. What does this port do/where does it go?
    2. Is it a problem that the float bowls I have do not cover it? (Are these the wrong bowls for these carbs?)


    Basically I'm trying to figure out if this is just some weird quirk of design updates/development and is totally normal (was used on a legacy design, or in other models, etc that share the same carb body, something like that)? Or if there is a problem here and I need to address it? any info is apprecaited!
    Last edited by RocketScientist; 06-25-2021, 02:37 PM.
    Tags: None
    #2
    Maybe the holes got eliminated...here’s a set minus the holesBD0FE275-0C47-4818-954D-C070964683D6.jpg
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

    Comment

      #3
      Might be a hole for a jig?
      1983 GS 550 LD
      2009 BMW K1300s

      Comment

        #4
        Originally posted by tom203 View Post
        Maybe the holes got eliminated...here’s a set minus the holes
        Yeah the various photo/video guides to cleaning and tearing down these carbs (like the one here at GSR) all show that style, without the hole. I'm just wondering why mine has it/what it does, and if I need a different float bowl to match with it? Though digging into the factory service manual, the pictures all show that hole being there, and in the one photo showing that area with the float bowl installed, it LOOKS like it matches what I see on mine. That is, you can see the tab on the gasket sticking out to go around the partially-exposed hole, but the float bowl doesn;t have a matching "kickout", and just half-covers it? It's not super clear in the image, but it makes me think this is maybe the way it is supposed to be?


        Comment

          #5
          i suspect it's an air bleed intake point. You'd need to compare the air intake side of carbs with and without the hole to confirm it.
          Commonly, the air bleed intake is one of the openings in the bottom of the intake bell. If one is blanked off on yours, the air has to come in from somewhere for that circuit.

          Comment

            #6
            Yeah that would for sure spark my interest as well, pretty fair to assume that if the manual shows it then you've got the right carb and float bowl setup for that bike.
            1980 Yamaha XS1100G (Current bike)
            1982 GS450txz (former bike)
            LONG list of previous bikes not listed here.

            I identify as a man but according to the label on a box of Stauffers Baked Lasagne I'm actually a family of four

            Comment

              #7
              This may help, but it is a BS32 carb.

              Idle mixture question - The GSResources Forums
              https://www.thegsresources.com/_forum/showthread.php?252329-Idle-mixture-question/page2
              Place your GS carburetor, fuel or exhaust questions in this forum.
              Jim, in Central New York State.

              1980 GS750E (bought used June,1983)
              1968 CB350 Super Sport (bought new Oct,1968)
              1962 CA77 305 Dream (bought used Feb,1963)

              Comment

                #8
                Originally posted by pdqford View Post
                This may help, but it is a BS32 carb.

                https://www.thegsresources.com/_foru...question/page2
                Exact same scenario as me. Well at least I know I'm not the only one to wonder about this. I went ahead and re-assembled mine and the bike is running fine and dandy now. So looks like that port/hole serves no purpose, at least not in this carb configuration or at this point (maybe a vestige of manufacturing?). My guess is it serves SOME purpose on SOME verison of this same carb body, otherwise why would the correct OE gasket for it have a cutout to seal around it? Regardless of the mystery, bike is running happily, so im happy

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