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Kawasaki GPX250 RPM changed unexpectedly

Discussion in 'Technical and Troubleshooting Torque' started by POW365, Feb 15, 2013.

  1. Hi,

    I have noticed that my GPX250 has been feeling a bit strange lately.
    At times I feel like it is fighting against me when I want to speed up.
    Biggest thing I noticed today though was that the RPM has changed.
    When I use to maintain a speed of 80km/h my taco read 6000 rpm in top gear (5th).
    Today when at the 80km/h mark my taco read less (around 5500 rpm).
    What has happend?
    Can something have changed on its own?
    Its it some thing to worry about?
  2. Have you had a new rear tyre fitted recently?

    The original rear was I think a 130/80/16. But you can fit a 130/90/16 which makes the gearing slightly taller & lowers your RPM at the same speed. Makes it accelerate slightly slower too.
  3. Brake (especially rear) sticking?
    Put it up on a stand and spin the rear wheel while working the rear brake.
  4. My old GPX250 had six gears, not five. That was an '88 model though so I don't know if things have changed since then. Other than that it's odd for the revs at a certain speed to go DOWN.

    edit: actually everything I read says six gears for the current one and every one before. Are you sure you didn't just discover top gear?
  5. My mistake. 6th is top gear. I did have a new rear tyre fitted recently. That could well be the reason. I will have to check the rear brake issue. But it does seem more engine related. Sometimes it's a smooth ride and other times there is a lot of vibration and engine braking.
  6. If the new tire is badly balanced it would explain odd vibrations as would a chain with bad tight spots in it or even one spark plug breaking down intermittently or losing fuel supply to one carb.
  7. Thanks. I will have a look at all those things.
  8. Rear brake won't affect speed/RPM ratios, but different profile tyres can, as can changing sprocket sizes (front & rear) & clutch wear. If it was the clutch, I would expect the revs to up, so it's probably not that.

    Are you sure it's the same gear?