Stuck/Frozen carb butterfly valve

Discussion in 'Motorbike Technical Discussion' started by jrallen, Dec 13, 2005.

  1. jrallen

    jrallen Guest


    I'm working on a '94 Honda VFR750 that has been sitting a couple of
    years. The throttle was stuck closed, and some digging around showed it
    to be one of the throttle butterflies. It has some hard varnish on it
    and is a little darker than the others. Inspection of a float bowl
    reveals only some varnish depositsn nothing green or growing. I've been
    doing my reading and have a couple of spray cans of Berryman B-12 at
    the ready, but I'm hesitant to just spray it all over everything for
    fear of damaging the rubber bits that may be hiding in the throttle
    shafts. So far, I've sprayed a little bit in the venturis and tried
    soaking the butterflies with WD-40 as well, but nothing's budging.

    Do I need to bite the bullet, break the carbs apart and tank clean
    them, or is there a less invasive option?
    jrallen, Dec 13, 2005
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  2. jrallen

    CK Guest

    B-12 won't hurt any rubber part that hasn't already perished from
    drying out and is already crumbling. Rubber diaphragms that have been
    cleaned with B-12 will soften and swell, then they return to normal
    size. I've been cleaning carburetors with B-12 for
    30 years now and have never damaged any rubber parts with it.
    If the carbs are off the machine don't break the individual carbs apart
    from the cluster.
    Keep the shafts all clamped together and the carbs attached to whatever
    brackets they
    are bolted to, but strip the brass parts out and spritz through all the
    orifices and passages.

    I've never seen a carburetor in such bad condition that it needed to be
    cleaned in a tank and gawd only knows what kind of acids or caustic
    solutions are in tanks intended for cleaning automobile carburetors.
    Part of the carb rebuilding process is
    chemical etching or chemical polishing to remove corrosion and whatever
    chemical is in there might remove metal from the precision drilled
    orifices in the carburetor body.
    CK, Dec 13, 2005
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  3. jrallen

    jrallen Guest

    Thanks for the vote of confidence. I went back and looked the butterfly
    over again, and this time looked at it from the top by retracting the
    slide. It did have a little bit of green corrosion around its rim. I
    believe it's either frozen around the rim or in its pivot shaft. I
    sprayed some B12 in and tilted the carbs so that the B12 is pooled over
    the pivot shaft and will let it soak that way for a day. If it's still
    not free, I'll soak the opposite side of the pivot shaft.

    I'm hesitant to apply any significant pressure to the throttle
    connection out of fear of bending some very precise parts. Short of
    directly whacking the butterfly with a mallet, what's the best way to
    get it loose? Keep spraying and soaking?

    jrallen, Dec 13, 2005
  4. jrallen

    CK Guest

    Have you tried turning the master idle knob clockwise to see if the
    butterflies move?

    Another way would be to put a small crescent wrench on one of the
    clamps that attaches the two throttle shaft together and gently turning
    the shaft.
    CK, Dec 13, 2005
  5. jrallen

    Matt Guest

    Are you sure the throttle cables aren't siezed up?

    If the cleaner is going where it should go, the throttle shafts will
    easily be cleaned of gum and varnish. You could try spraying the shafts
    from the insides of the carbs---maybe that's what you mean by "soak[ing]
    the opposite side of the pivot shaft".
    Matt, Dec 14, 2005
  6. Generally I like Kroil for frozen parts. Might be more effective
    than carb cleaner. I don't think you'd have trouble with rubber bits.
    Kroil is a pentrating oil.
    If you're sure you're trying to turn it in the right direction, you're
    dealing with a mechanical problem and should treat it as such.

    Can you remove the throttle linkage, put a well fitting wrench on
    the shaft end and apply some very mild torque ?
    Rob Kleinschmidt, Dec 14, 2005
  7. jrallen

    jrallen Guest


    Matt: no, it's not the throttle cables. That's the first thing I
    checked. I have the carb assembly off the bike now.

    I sprayed and soaked the shaft some more tonight, then did as Rob
    suggested to take some of the throttle linkage out of the equation: put
    a wrench on the nut at the end of the throttle shaft that the stuck
    carb was on and slowly twisted.

    Nothing popped; it just slowly opened and...stayed where I left it. I
    kept spraying, soaking, and turning the shaft until I could do it by
    hand. Things eventually worked free to the point that the return spring
    was actually closing the butterfly. From that point, a few minutes of
    working the shaft back and forth had it snapping right back like it

    Now on to actually cleaning the carbs...

    By the way, I did notice that the B12 was dissolving the toothbrush I
    was working with, so I'm still going to try to keep it away from the
    rubber parts.

    Thanks everyone for your help!
    jrallen, Dec 14, 2005
  8. jrallen

    Ron Seiden Guest

    1. The ingredients list on B-12 is remarkably similar to that of lacquer
    thinner -- my favorite universal cleanser. However, some of those
    ingredients *will* dissolve cheap plastics (like that toothbrush). Almost
    any part meant to be in a carb will not be affected.
    2. If you do remove small parts from the carbs, keep track of which carb
    they came from -- Can't guarantee it, but it's likely that they will be more
    "comfortable" going back in the same holes they came out of...
    3. Kroil is an *extreme* penetrating oil. For mechanical parts that need
    freeing, it will do miracles. (It's so good that many rifle nuts use it for
    cleaning their barrels -- it can actually get under a lot of the stuff
    that's been heat & pressure deposited on the steel...)
    Ron Seiden, Dec 14, 2005
  9. Glad you're moving ahead.

    You probably ought to just replace the rubber parts. I can't imagine
    the O rings or diaphragms being in very good shape after sitting
    so long.
    Rob Kleinschmidt, Dec 15, 2005
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