buddies bike has a bad flat spot right in the middle of the powerband...
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Thread: buddies bike has a bad flat spot right in the middle of the powerband...

  1. #1
    ninja machinist Array Darkcbr's Avatar
    Join Date
    Apr 2004
    RC-51, KX250

    buddies bike has a bad flat spot right in the middle of the powerband...

    I'm curious as to what could be the cause. The bike is a '82 Kawasaki GPZ550. It has an MAC pipe on it which is aftermarket. When accelerating it pulls well initially but right at about 5400-5500 the bike doesn't pull as hard. When the revs get past 6500 it comes alive again and hauls all the way to redline which is about 9000rpm approximately.
    Could a shop fix this? Will it be expencive?

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  3. #2
    Moderator Array TeeTee's Avatar
    Join Date
    Feb 2002
    Out to pasture in the 'Wack
    04 Kawi Z1000,
    With the Macs pipe and perhaps a couple of other mods it may be in need of a jet kit. Or he may get away with just shimming the needles or altering the float level a little. Either way it needs a tuner to work with it.

    It also means more than one trip into the carbs so if you have a mechanic doing the work it could get quite expensive. If he can do it himself it's just a lot of time.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  4. #3
    this is my...boomstick! Array CrotchetyRocket's Avatar
    Join Date
    Aug 2002
    click, click
    Barring anything else being wrong, the needle transition is probably to shallow for the air demands of the engine. A change of needle and seat, or a raising of the needle may help with mid-range flat spots.

    A 1000 rpm flat spot is pretty bad. I'd be disassembling the carbs and making sure everything was actually all right in there so, I'm not trying to tune around a mechanical problem. A good example is the needles in old bikes wear themselves and the seats pretty badly and can lead to all kinds of mixture mess ups.

    It could be expensive if a shop looks into this, as there's no way of knowing what's actually wrong.


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