Intermittent missing after idling period - Solved.

Discussion in 'Motorbike Technical Discussion' started by Doug W, May 3, 2012.

  1. Doug W

    Doug W Guest

    Here's a bit of on-topic post.

    97 ZX-11. After a short stop at a light, or after initial startup, it
    sounded as if it was missing one cylinder. Occasionally, after normal
    road speeds and another stop, the issue disappeared, only to return at
    the next stop

    Also, if I let it idle in this state for a time, then pull the plugs, #1
    was loaded with soot. (running rich). I could also smell the richness
    in the exhaust if the wind was blowing in the right direction.

    Since I had let the float bowls dry out some time ago, and spent
    considerable time trying to clean them, I assumed there was still some
    junk remaining in the passages. I cleaned them many times, especially
    #1. I must have had the carbs out 10 times.

    I even checked the float bowl fuel level via the clear hose method.. All
    were good.

    On the last cleaning attempt, I removed everything I could, including
    the float needle valve. The tip of the needle looked a bit dirty, so I
    wiped it off, but didn't look too closely at it.

    After that, it ran much better, but still loaded up far too often.
    Since one of the things I messed with was the needle valve, I formed a
    theory that the float level was unstable due to the valve not seating
    fully. It leaked, letting the fuel level climb too high at idle,
    causing the richness. At speed, the fuel consumption was high enough
    that the leak had little effect.

    I took a closer look at the needle for #1 carb:
    Not good..

    Fortunately, a spare carb from my old 750 Interceptor was the same type,
    and in much better condition, so I dropped it in, and.. Problem solved!..

    Just in case, I bought a new set, and the photo shows the bad, and a new
    one (to be installed this week-end).

    I've always thought of float needle issues as complete failure to seal,
    where gas leaks out of the carb when parked, eventually flooding the
    engine, or making a puddle on the ground. In this case, as the fuel
    level rose beyond the normal level, the increased push from the floats
    must have sealed it each time, stopping the flow.

    When I measured the float bowl levels earlier it must have sealed
    properly that time.
    Doug W, May 3, 2012
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  2. Doug W

    Mark Olson Guest

    Does the fuel pump on your bike stop fuel flow when it isn't running?
    It doesn't appear that your bike has a vacuum petcock, which is what
    Kawasaki normally fits to their carbureted bikes. For carbs to overflow
    as you describe, their float needles have to leak AND the petcock has
    to be left on (if a manual petcock) or the vacuum shutoff valve in the
    petcock has to have failed.
    Mark Olson, May 3, 2012
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