trouble starting when warm

Discussion in 'Motorbike Technical Discussion' started by troubled, Jun 25, 2006.

  1. troubled

    troubled Guest

    I recently bought a 86' ninja zx600. When it is cold I can get it to
    start with the electric ignition, but after it warms up it won't fire
    over. If I push it when it is warm and won't start electronicly, it
    will fire right over. any help? could this be a valve problem
    troubled, Jun 25, 2006
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  2. Could be, yes. Could be a coil breaking down when hot, as well.

    Try it with some new plugs first (cheap solution, and one that works
    surprisingly frequently).
    The Older Gentleman, Jun 25, 2006
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  3. troubled

    FB Guest

    It wouldn't hurt to check the valve clearances. If they have tightened
    up, the clearance
    necessary to allow the valves to seal in compression may be gone.

    But, while you have the gas tank off to check the valve clearances,
    look carefully at the carburetors to see if the EPA anti-tamper plugs
    have been drilled out.

    If you can see the slot-headed idle mixture screws, you know that some
    shade tree mechanic has been tampering with the mixture screws. Shade
    tree mechanics usually don't have a clue about the idle mixture system,
    they always turn the screws too far counterclockwise and the engine RPM
    slows down, so they adjust the master idle knob to make the engine idle

    This opens the throttle butterflies slightly and that reduces engine
    vacuum downstream of the butterflies and defeats the "choke" system.

    Your carburetors do not have a real choke, there is no choke plate.
    Instead there is a starting enrichener system that is a little valve in
    a bypass passage. When you turn the handlebar-mounted "choke" lever to
    the ON position (or pull it sideways if its a "choke" knob) airflow
    through the bypass passage sucks gasoline straight out of the float

    But, if some shade tree mechanic has screwed up the idle mixture screws
    and turned up the master idle knob to compensate for his screw up, the
    starting enrichener is defeated.

    You can go to or to look at
    carburetor parts diagrams. The idle mixture screws are probably
    underneath the carburetors, forward of the float bowls, or they may be
    on top, downstream of the butterflies and forward of the diaphragm
    chamber caps. If you can see slot headed screws there, Joe Shadetree
    has screwed up your idle mixture.

    OTOH, if you see a round cap in that area, nobody has ever messed with
    the idle mixture screws. However, that is not necessarily a good thing.
    The idle mixture passages and ports may be gummed up and partly

    I recommend mixing about three ounces of Berryman's B-12 Chemtool Choke
    and Carburetor Cleaner with a full tank of gasoline and going for a

    B-12 is very available in the USA. You can get it in liquid form or an
    aerosol can for about $3.00. B-12 contains xylene, actetone and methyl
    alcohol and quickly cleans out the tiny idle passages and ports. if you
    can't find B-12, STP or Gum Out carburetor cleaner will work, but B-12
    is the only one I know of that you can get in liquid form.

    After you have ridden slowly for some miles with B-12 in your tank, you
    may notice that the engine idles a lot faster, that's normal if the
    idle passages were plugged up and somebody turned the idle speed up to
    compensate for dirty passages, so you will have to turn down the idle
    RPM knob.

    Check the diagrams on the sites I mention to see where the knob is, or
    look in your owners manual. The knob is probably between the # 3 and #
    4 carbs, the # 4 being the one on the right, unless the knob is on a
    cable. In that case, the knob will be on the left side of the frame.
    FB, Jun 25, 2006
  4. troubled

    OH- Guest

    What the others seem to ignore is that your bike starts just
    fine if you push start it.
    To me this indicates one or both of two conditions - a weak
    battery or a rich idle mixture, possibly made worse by bad
    spark plugs.

    Are your plugs very sooty after low speed riding and idling?
    Check your air filter and try increasing the throttle opening
    (the idle adjuster) to let more air in if your idle RPM is on
    the low side. See FB's post for more details.

    With a good battery, sparks can be strong even on dirty
    plugs and when the starter motor is running and might
    manage to ignite even a very rich mixture, that's why I
    mentioned the battery.
    N.B. New plugs will soon be bad plugs if your idle mixture
    is too rich.

    As one of my bikes have no electric starter, no battery and
    is damn hard to push start I know the importance of a clean
    air filter and a good spark plug. Kicking an engine into life is
    no fun after the first minutes.
    OH-, Jun 25, 2006
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