mikumi carbs

Discussion in 'Motorbike Technical Discussion' started by spud, Sep 29, 2005.

  1. spud

    spud Guest

    I have a GS750 1977, the engine is from a 1978 bike and the carbs are o
    my original engine, where can I find out the carb settings for them, a
    I have inadvertantly adjusted the screws on the bottom of the carbs an
    Iv'e been told that one of these is the fuel metering screw....
    Can anyone help
    I found this forum by looking for mikumi carbs,
    Hello to all......
    spud, Sep 29, 2005
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  2. spud

    jamison Guest

    I would check out the forum at www.thegsresources.com . There are some guys
    on there (Keith Krause, Earlfor, just to name a few) that know the Mikuni
    VM-series carbs that you have like the backs of their hands.

    I have the same model/year bike as you. I can tell you that generally, the
    fuel mixture screw on the bottom front of each carb should be roughly 1-1.5
    turns out if the bike is stock. You want to make sure that when you are
    tightening these screws to seat them LIGHTLY. Ever so lightly. Reason being,
    this screw comes to a very sharp tip up inside the carb body and if you
    tighten it in, the tip can break off and cause NIGHTMARES. Just believe me
    when I say I have been there ;-).

    The GS Resources is a wealth of info for these bikes. I would definately
    recommend checking out the forums.
    jamison, Sep 30, 2005
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  3. The original equipment carburetors on the GS750 were slide valve
    carburetors. If you go to www.partsfish.com and register, you can look
    at the carburetor fiches and see what I mean.

    The idle mixture screws are called "pilot air screws". They are NOT on
    the bottom of the carburetors. They are on the sides of the
    carburetors, pointing down at a 45 degree angle. (1)

    This makes it really easy to squirt aerosol carburetor cleaner through
    them if the idle mixture ports get plugged up.

    Since they are AIR screws, turning them clockwise makes the mixture
    richer, turning them counterclockwise makes the mixture leaner. About
    turns from fully closed should do the trick.

    (1) That business about you adjusting the screws on the BOTTOM of the
    carbs makes me wonder just what the heck you were turning. The drain
    in the bottom of the float bowls?
    krusty kritter, Sep 30, 2005

  4. Google must be even better than I thought, then.... ;-)
    chateau.murray, Sep 30, 2005
  5. spud

    VM Guest

    For someone who comes across like a complete asshole who thinks he knows
    everything about motorcycles, you have proven that you are exactly that.

    The screw he is talking about is the Pilot Fuel Screw. It, along with the
    AIR SCREW you were talking about, determine how much air and gas are used in
    the pilot circuit. Here's a picture of what it looks like:


    and here is where it goes on the carb:


    Krusty, feel free to not give us one of your 500 word minimum posts when you
    have no clue WTF you are talking about.
    VM, Sep 30, 2005
  6. Find a message where I said that I know "everything about motorcycles"
    and provide a link to that message.

    Why are your panties all in a knot over my reply to the OP and my
    asking about what screw he was turning? That screw certainly does NOT
    appear on the parts fiche for a slide valve carb from a 1977 GS750.
    That part could be from an aftermarket rebuild kit. Provide a link to
    the vendor original photograph.
    Post a photograph of the carburetor in side view so we can all see if
    the nasty dirty carb you took a picture of is the slide valve carb from
    a 1977 GS750 or or it's actually a CV carb from a 1980-ish GS750.

    Come on, now. Enquiring minds want to know what's going on here.
    krusty kritter, Sep 30, 2005
  7. spud

    . Guest

    Here you go, from when I got the carbs from a bike that had sat outside for
    a few years without being touched, to a complete clean/rebuild:


    I realize that they do not show this screw on any parts fische because I
    have had to replace one and only certain rebuild kits contain this screw. My
    point is that next time, instead of just simply stating that the screw
    doesn't exist because you can't find it on a fische, realize that maybe it
    is something that you don't know about and shouldn't be giving someone false
    information. Maybe it's possible that since the screw was supposed to be
    capped from the factory due to emissions requirements, Suzuki chose to not
    show them on any parts fisches/lists. Who knows. But it sure exists and your
    post would have just further baffled the original poster if there wasn't any
    ., Oct 1, 2005
  8. Your pictures don't actually *show* the screw installed, and whether
    it's externally accessible with the float bowl still installed. I found
    *one* message on Usenet where an owner asked about a mixture screw that
    was *inside* the float bowl. Nobody answered that message, either
    nobody knew the answer, or nobody was interested enough to reply.
    False information? Why would I intentionally give somebody false
    Why do you even accuse me of giving false information after I went out
    of my way
    to help somebody who asked for information? I asked the OP for more
    about what screws he was turning, and I got a rude response from *you*

    All information is "good" information, but sometimes it's not the
    information the questioner is looking for. Maybe learning that there
    was an oddball slidevalve carburetor with fuel mixture screws in the
    float bowls will help somebody else what owns a 28 year old motorbike.

    Now I've seen *two* kinds of slide valve carbs with mixture screws that
    might be called "gas screws". Mikuni radial flatslide carbs also use
    "fuel air screws" instead of "pilot air screws".

    But there's no need to be so nasty about it. You actually went through
    all that trouble just to prove that krusty kritter was wrong about
    something. You had to
    digitally alter an image just to prove it. What was *so* important that
    you had to do *that*?

    Why couldn't you just say, "No, there was *one* year of GS750's that
    had a pilot gas screw, here is a picture."?

    The parts fiches on www.partfish.com and www.bikebandit.com do not
    include the 1977 GS750B carburetor, they show the 1978 GS750C carb and
    go from there.
    krusty kritter, Oct 1, 2005
  9. spud

    randyshipp Guest

    Not sure what the problem is, but GS Resources seems to be down. Not
    sure if they missed a payment for their hosting or what. Hopefully
    they'll be back in business soon, as I just bought a 1980 GS850GL over
    the weekend.

    randyshipp, Oct 11, 2005
  10. The URL is something like "thegsresources.com" not just
    "gsresources.com". I can see where people think they are getting into a
    motorcycle site and search it for Suzuki information.
    krusty kritter, Oct 11, 2005
  11. spud

    mdteek3 Guest

    Guys yes indeed their is bottom mounted carb mixture screws on my original 1977 gs750 B model and I also need to know where to set them.

    Thanks for the help if anyone knows.
    mdteek3, Jul 15, 2015
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