What are these holes for?

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  • oldsecret
    Forum Newbie
    • May 2025
    • 8
    • Norway
    #1

    What are these holes for?

    Hello.
    I'm a noob when it comes to motorcycles. Never ridden one, never done maintenance/repair on one. But now I own one and its old plus it doesn't start.
    It's a 1977 GS400 caferacer project that I bought cheap because I didn't have enough projects going on. I figured it would be fun to learn something new. Right.
    So, I started with ripping out the twin BS34 Mikuni carburetor, took them both apart and cleaned them up quite nicely. Reassembly was ok.

    BUT, now there's a little hickup. There are two holes or outlets that's supposed to have tubes connected to them. One on each unit. Blue circles on the picture. I have searched online and in manuals to find an explanation on their purpose but so far no luck. The red circle is where to fuelhose goes from the petcock I assume.

    Can anyone give me some information please?
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    • chuck hahn
      Forum LongTimer
      Past Site Supporter
      • May 2009
      • 25918
      • Norman, Oklahoma
      #2
      Are you sure they are actually holes? As i recall there are no nipples for drains or vacuum. They are probably casted but not drilled.
      MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
      1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

      NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


      I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

        Comment

        • oldsecret
          Forum Newbie
          • May 2025
          • 8
          • Norway
          #3
          I'm pretty sure they are open nipples. They're not casted.
          Since they are on the "air" side of the carb I could guess they might have something to do with vacuum.
          There is a vacuum connect on the front left side that has a hose going to the engine.

            Comment

            • zed1015
              Forum Mentor
              • Oct 2020
              • 411
              • North Lincolnshire - UK .
              #4
              The brass outlets are simply float bowl breathers and should be kept open to atmosphere with some open ended hose attached which either connects to the original airbox or hang down behind the rear of the engine.
              Mikuni Viton Choke Plunger Seat Renewal.
              VITON Choke plunger seals .KAWASAKI Z1,Z900,Z650,Z1000,Z1R,SUZUKI GS1000,GSXR,RF | eBay

              Air Corrector Jets for Mikuni VM 24, 26 and 28mm carbs .
              https://www.ebay.co.uk/itm/254380193...84.m1555.l2649



              sigpic

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                • chuck hahn
                  Forum LongTimer
                  Past Site Supporter
                  • May 2009
                  • 25918
                  • Norman, Oklahoma
                  #5
                  OK.. Guess i need to hit the dollar store and replace the ones that got crushed yesterday. Stuck them where i always do when riding the KZ but they blew off. Went back and they had already been run over.
                  MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                  1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                  NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                  I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                    Comment

                    • oldsecret
                      Forum Newbie
                      • May 2025
                      • 8
                      • Norway
                      #6
                      Thank's for the replies. Breathers I can handle :-D

                        Comment

                        • Rob S.
                          Forum Guru
                          Past Site Supporter
                          • Dec 2013
                          • 9393
                          • New York City
                          #7
                          Originally posted by zed1015
                          The brass outlets are simply float bowl breathers and should be kept open to atmosphere with some open ended hose attached which either connects to the original airbox or hang down behind the rear of the engine.
                          Agreed. They frequently run to near the swing arm pivot.
                          1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

                          2016 XL883L sigpic Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

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