Brmm. Brmmmm. Pop!

Discussion in 'Classic Motorcycles' started by RG, Sep 3, 2003.

  1. RG

    RG Guest

    The old Thunderbird seems to be going nicely now with just a minor niggle.
    After a good blast, on switch off whilst parking up, she tends to have a
    little spit or two back through the carb. This sometimes happens on kicking
    her up too.

    Nothing major here but I was wandering if it was likely to be a mixture
    issue as the exhaust emission seems to be faintly smokey too - more so when
    cold. Not oily blue or anything like that, just mucky.

    After the blast too, the tick-over can dip to near stall then struggles back
    to normal. A pop or two can accompany this.

    She's fitted with and Amal Mk 1 concentric to replace the original monoblock
    (she's too young to have had an SU)

    Maybe the simpler concentric is inferior to the monoblock and not as fine in
    operation?

    Anyone got a tenpenn'orth to chuck in here?

    Roger
     
    RG, Sep 3, 2003
    #1
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  2. RG

    Andy Clews Guest

    Thus spake RG unto the assembled multitudes:
    It's 25 years since I had a Triumph twin but my Tiger 650 used to do that
    quite a lot. Occasionally it would run on a few turns when the ignition
    was switched off. Wonder if it could be carbon buildup causing hot spots?
    The starting kick-back could be quite vicious too. Neither of these used
    to bother me; I just put it down to 'character'.

    I had a C15 once which often spat back through the carb. Once the damn
    thing nearly went up in flames when a spit-back ignited petrol in the carb
    mouth and a flame licked up around the fuel tank. I flapped at it madly
    with a glove and swatted the flames out, but it could have been nasty ;-)
     
    Andy Clews, Sep 3, 2003
    #2
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  3. RG

    sweller Guest


    I too had a C15 that did similar. It also had the turret/distributor
    type points housing which, as usual, had worked loose the splined fit
    between the points housing and drive shaft tunnel clampy bit. Causing
    the timing to wander randomly.

    Eventually cured by driving hard steel pins down undersize holes at the
    housing/tunnel interface.
     
    sweller, Sep 11, 2003
    #3
  4. RG

    sweller Guest


    Popping in the carbs is, IME, normally ignition related. The dirty
    exhaust, as you said, points to an over rich mixture, as does the
    fluffing at idle. Does it start easily from cold?

    You may have two problems compounding one another.

    Set the tappets, ignition (and a new plug), clean air filter and set
    float height. Basically get the settings to a known good base and see if
    that cures it. Or exposes other problems, such as a deliberately over
    rich mixture to overcome an air leak etc.

    Remember, in a lot of cases changing one may impact on another.
     
    sweller, Sep 11, 2003
    #4
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