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Thread: Carb sync - feeling a bit dumb.

  1. #1

    Carb sync - feeling a bit dumb.

    I was getting ready to sync my carbs with a fancy new carb sync gadget that I just bought. I went to hook it up and I can’t find any vacuum ports. Not one vacuum hose. Is it my imagination - or does my 1979 R100RS lack a vacuum connection?

    I appreciate all your help.

  2. #2
    Quote Originally Posted by mxg3 View Post
    I was getting ready to sync my carbs with a fancy new carb sync gadget that I just bought. I went to hook it up and I can’t find any vacuum ports. Not one vacuum hose. Is it my imagination - or does my 1979 R100RS lack a vacuum connection?

    I appreciate all your help.
    You should find a small tube with a screw into the tube end. It will be either on the bottom of the carb or on the side. Remove the screw and insert the carb synch instrument hose over the end of the vacuum takeoff stub.
    Last edited by PGlaves; 05-22-2020 at 02:00 PM.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
    Liaison 20774's Avatar
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    Here's a couple of threads/pictures that show where the vacuum port might be:

    https://forums.bmwmoa.org/showthread...-Carb-Question

    See the shots with the horribly stained floats in the next link...part way down the page? There are two screw heads. The larger one is the idle mixture setting. The smaller one is the vacuum takeoff port.

    http://home.insightbb.com/~cdpumphr/...les_page_3.htm

    Here's a picture with the port on the side:

    https://forums.bmwmoa.org/showthread...vacuum-problem
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    Quote Originally Posted by PGlaves View Post
    You should find a small tube with a screw into the tube end. It will be either on the bottom of the carb or on the side. Remove the screw and insert the carb synch instrument hose over the end of the vacuum takeoff stub.
    It is possible that the stubs are there but are covered with plastic or rubber caps. It is also possible that the stub is there, open, creating a vacuum leak.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  5. #5
    #4869 DennisDarrow's Avatar
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    Can't find anything about the bike you are riding or possibly just talking about......Anyway, been a few nights of sleeping since I worked on my early /5 but seems that these did not have a port for you to hook up a hose/instrument to. If it's that way, you are stuck being handy with your ears and the shorting method. Which, actually are just as good as the high dollar tubing/ATF/yardstick instrument that I have down in the shop...…...maybe check out filling out your profile???????????.....Dennis

  6. #6
    Quote Originally Posted by DennisDarrow View Post
    Can't find anything about the bike you are riding or possibly just talking about......Anyway, been a few nights of sleeping since I worked on my early /5 but seems that these did not have a port for you to hook up a hose/instrument to. If it's that way, you are stuck being handy with your ears and the shorting method. Which, actually are just as good as the high dollar tubing/ATF/yardstick instrument that I have down in the shop...…...maybe check out filling out your profile???????????.....Dennis
    Real OEM shows the carbs on this bike to be Bing 94/40/107 and ...108, with the take off port on the side.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  7. #7
    Quote Originally Posted by PGlaves View Post
    You should find a small tube with a screw into the tube end. It will be either on the bottom of the carb or on the side. Remove the screw and insert the carb synch instrument hose over the end of the vacuum takeoff stub.
    This was what I found. I removed the screw and connected the syncing tool. Thanks for the help.

  8. #8
    #4869 DennisDarrow's Avatar
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    Quote Originally Posted by PGlaves View Post
    Real OEM shows the carbs on this bike to be Bing 94/40/107 and ...108, with the take off port on the side.
    Duhhhhh…..Golly Paul, what would I do without you there to edit and correct........….there It was right there in his comment to us all about the bike that I needed to know...……..lol....Thanks Bud......

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