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Engine power issues, or flat spot for speeds > 0km

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Gef, Feb 10, 2008.

  1. Tired old zzr250 which I only still have because I can't currently afford an

    While riding to a friends, no obvious issues with the running of the bike, I took off from the lights without as normal and caught up with the traffic and
    suddenly the power output from the engine went to about 1/3 of the normal
    output. I pulled over and looked over the bike, not sure what I expected to
    see, but everything sounded fine, and the revs sounded smooth. It just wasn't converting that noise into power.

    My initial thought was that there was a spark issue, so I pedaled the bike (well, rode it at pedal pace) to my friends where I pulled off the tank &
    checked the plugs. Both exhaust pipes were hot, and the plugs looked fine
    so, nothing obvious there.

    I had to get the bike home, so rode it in it's current state a total of about
    25-30kms with no change.

    I've checked the fuel lines, and they are all straight without kinks, the inline filter, which has always been there, was clean and about 80% full of
    fuel. So it seems fuel is getting _to_ the carby without issues, Though I
    didn't try turning the choke on while riding it to see if it wasn't getting the
    fuel it needed

    If it was water in the tank, I would have thought that would have had
    a more dramatic affect (coughing & spluttering). I'm assuming that I'll
    have to pull the carby off & clean whatever gunk has accumulated there.

    I'm capable with a spanner, but no mechanic, so any ideas / tips?
  2. drain the carbies for starters, see if there is water in them
  3. Check the compression, you may have done a head gasket, symptoms sound like you've dropped a cylinder.

    Had the same happen in the old car the same way, pulled down to the lights fine, driving sedately, took off, and lost half the power.

    I did the same as you, checked the spark plugs for immediate problems, no hassles, wasn't til I had two cylinders showing 270kPa apiece it was obvious, only in your case, it'll be one cylinder down on compression. (I got $300 from the cube factory for that shitheap... :twisted:)

    Take the plugs out and dry crank it tomorrow, before you start it just in case. Had a friends EF falcon almost take my ear off as it sprayed water next to me when I removed the plugs to crank it, cracked head and a cylinder filled with water after sitting for an hour to cool down. if you get it running, check the radiator for bubbles. [means that the head is forcing air/fuel into the system, if the ZZR is watercooled, but oil can cause as much damage, so do it either way]

    It may seem like it's running normal, and it is - fuel is still being burnt, however the pressure is escaping the cylinder