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Help ZXR250 A Model Engine in C Model Frame

Discussion in 'Kawasaki 250cc In-line 4's' started by Khaiden Cori, Jul 24, 2017.

  1. kiffsta

    kiffsta Senior Member

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    IMG_1299.JPG

    Here is where the speedo plugs into the cluster, I had to remove the yacht to get access
     
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Hmm, just read up on the resistor / derestrict mod using the 1 watt 10,000 Ohm (10k Ohm) resistor which run's from the pink wire to an earth point, with the 3 terminal plug/socket unplugged from the back of the speedo
    10k Ohm 1 watt resistor

    Does the ignition just cut out at 180km/h ?
    If so the circuit board must be powered by the brown wire and earthed my the black w/yellow.
    It must supply 10k Ohm's to the cdi but when the speedo reach's 180km/h it cut's the circuit to the cdi
     
    Last edited: Jul 25, 2017
  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Let's look at this logically... break it down piece by piece

    What's non-standard on this bike - the motor, obviously.

    What's different between the motors? Bore and stroke.

    The bore to stroke ratios are different

    A model: 48 / 34.5 = ratio of 1.39
    C model: 49 / 33.1 = ratio of 1.48

    This can drastically effect the required ignition timing for proper combustion. The TCI boxes will likely be programmed with different ignition curves, and this will likely be causing your hard starting and 16,000rpm limit. The fact that the speed limiter also limits you to 180km/h which is roughly 16,000rpm in top gear is seemingly a coincidence. If you change the front/rear sprockets you might even find you can hit the speed limiter at a lower RPM (if all else is working correctly)

    The fact that it runs at all is because the wasted spark system fires at top dead centre, no matter what stroke the cylinder is on. If this were a coil on plug system firing one cylinder at a time, you'd have no hope of it starting, and the possibility of causing damage by firing at the completely wrong time, because the TCI box is the wrong one for the motor. It'd be like trying to run a Yamaha FZR250 with a Honda/Kawasaki/Suzuki TCI - it's not going to work right, if it even works at all.

    The solution is that you run the correct TCI box for your motor. The additional problem is that the TCI wiring/pinout is different between A and C models. So you either have to wire it up correctly to the C model loom, or use all A model electrics, or swap the A model motor for a C model.
     
    Last edited: Jul 25, 2017
  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Coil on plug would still fire and run the same as the original 2x twin fire coil's, that system is running on my FZR with wasted spark
    The change's in bore/stroke ratio just move where the torque and power are made
    Oversquare engine's sacrifice low speed torque for rpm, so with the C engine being more oversquare it will rev better than the A engine, with lower piston speed, less stress on the bottom end and less friction

    I wouldn't think the timing would be that different between the 2x model's, but it'd be worth a try using the matching TCI to the engine
     
  5. Khaiden Cori

    Khaiden Cori Active Member Premium Member

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    I have an Mmax limiter on my C model plugged into the Speedo.

    Should I plug it into his bike and see if it makes a difference ?:)
     
  6. kiffsta

    kiffsta Senior Member

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    Yes
     
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  7. Khaiden Cori

    Khaiden Cori Active Member Premium Member

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    Hey guys so we got it too move up to 18k !
    Turns out the exhaust cam was a little out :/ and no exhaust gaskets

    Runs so much better noe and starts piss easy it just won't go past 18 :/ haha

    Gunna try my limiter box thing in a few days then if that doesn't work we will change jets as we have C model carbs on
     
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  8. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Well that certainly wouldn't have been helping, but no exhaust gaskets? That's a new one.

    What exactly is this limiter you're talking about? Never heard of such a thing before.
     
  9. Khaiden Cori

    Khaiden Cori Active Member Premium Member

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    Yeah the little rings where the exhaust system bolts onto the exhaust ports was missing so a bit of an exhaust leak

    Like kiffsta posted
    A limiter remover box that plugs into the Speedo to eliminate the restrictor when it gets to 180kmh
    Bike could be having a shitfit and thinking it's hitting limiter in each gear causing it to limit

    I have an Mmax one
    And kiffsta posted a posh red rev one :)
     
  10. Mr_Muddle

    Mr_Muddle Active Member

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    technically you are correct to a point. The limiter is for two functions. First is it checks for a speedo connected via pink wire, on the A loom it comes back into the CDI via Black/white, but pink on C. If the speedo is disconnected it will limit to 16k rpm. Once connected the limiter kicks in at 180kph, to get around it you need a 10k ohm resistor on the pink wire effectively, for me the easiest way to do it on my race bike was to connect speedo and disconnect cable from front wheel.
     
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  11. Mr_Muddle

    Mr_Muddle Active Member

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    Brown wire is main power similar to red wire.
     
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