Build custom airbox?

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  • benjo
    • Jan 2026
    #1

    Build custom airbox?

    Hi all,

    So I was one of the poor souls who decided to take off their airbox and replace it with pods (1981 GS450). I then built a shallow box out of metal in the same area that the old airobox was to put in all of my electrical stuff (RR, solenoid, indicator clicker, wires)...its welded in their so the possibility of putting the airbox back is not possible....so reason with me here.

    No surprise, but the airpods are tough. I have spent so much time re-jetting and adjusting, but the RPMs struggle if you give it a hard ref and it pops and burbs all over the place haha

    So, I have the bright (or completely idiotic) idea to build an airbox out of plastic that can fit in between my shallow electrical box and battery. So I guess my question here is: how important is the volume of the airbox, shape, etc in balancing the air/fuel mix? I am thinking that even if I can't get the completely right dynamic that it would atleast do a better job of creating the vacuum atmosphere needed, that the airpods are not doing at all, to properly lift the diaphram/needles to give a smoother ride.

    Thoughts?

    Thanks!
    -Ben
    Tags: None
    • tom203
      Forum Guru
      Past Site Supporter
      • Aug 2010
      • 8925
      • Norway,Maine
      #2
      I love ambition! Consider using an oblong airfilter spanning both carbs -this might duplicate what you are after in a small package. Lots of cars use this style , along with atvs, bikes,etc.

      image.jpg
      1981 gs650L

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

        Comment

        • Steve
          GS Whisperer
          • Jun 2005
          • 35924
          • southwest oHIo
          #3
          Originally posted by benjo
          So I guess my question here is: how important is the volume of the airbox, shape, etc in balancing the air/fuel mix? I am thinking that even if I can't get the completely right dynamic that it would atleast do a better job of creating the vacuum atmosphere needed, that the airpods are not doing at all, to properly lift the diaphram/needles to give a smoother ride.

          Thoughts?

          Thanks!
          -Ben
          It's not really so much that they need a "vacuum atmosphere" to operate. Yes, the opening of the stock airbox does restrict air flow a bit, which creates a bit of vacuum, but it's really more of having the boots smoothe the airflow going into the carbs. It is not the "vacuum in the airbox" that lifts the slides, it's the velocity of the air going through the carbs that does the lifting.

          To build a box, find a way to incorporate the stock boots, which are basically rubber velocity stacks that draw air from the airbox. It would also help to know what the size of the stock opening is in the airbox. That way, you could probably go back to stock(-ish) jetting.

          .
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            Comment

            • benjo
              #4
              Hi Steve,

              So I have ended with the craziest carb configuration for my 1981 gs450. I have the twin carbs with 45 pilots and 115 mains, and in the airpods I have put a penny washer with two holes drilled through it. Absolute maddness. Things brings me back to a question I posted on here a while back.

              There appears to be two different models of the Mikuni BS34ss carbs.
              One like this: https://images.cmsnl.com/img/partsli...ig-12_fb86.gif

              and one like this: https://images.cmsnl.com/img/partsli...ig-12_3696.gif

              The first one has the jets sitting in the bowl where the second one has the jets sitting in the body. I have the second sent of carbs. I took them off a GS750 which have a quad-rack of 34s. I took carb 1 and 4 and put them together to make a twin set. (It's tough finding parts in South Africa)

              So questions:

              1) Do these different carb types affect performance? even though the are both 34mm?
              2) You measure the size of the carbs by measuring the diameter of the inside of the carb that goes to the engine side, right?
              3) Do I have the wrong carbs for these things?!?!?!?!

                Comment

                • Guest
                  #5
                  I'm interested in seeing this set up. How are you hooking the throttle cables up? The throttle linkage mechanism in located on the #3 carb.

                    Comment

                    • benjo
                      #6
                      The pairing of carb 1 and 4 on the rack was pretty easy. The rack looked like this (not actual photo): http://www.motorsloop.com/images/suz...650GMKAT41.JPG

                      So I took the middle mechanism on the butterfly spring between 2 and 3 and moved it between 1 and 4. Pretty straightforward.

                        Comment

                        • benjo
                          #7
                          This is a bigger picture where you can see how easy it would be to move the throttle mechanism to other carbs.
                          http://www.motorcycles123.com/mc123_images/suzuki_carbs_lg.jpg

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