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Help zzr250 one cylinder when cold

Discussion in 'Kawasaki 250cc Twins' started by Martin Green, Dec 22, 2020.

  1. Martin Green

    Martin Green Active Member

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    evening all

    I have picked up a 93 zzr250 that has been standing for several years. I cleaned the carbs, changed the oil and installed new spark plugs. It started ok but only fires on one cylinder while its cold.
    If I warm it up the second cylinder fires up and it runs ok ( apart from a slight bogging down at 6k rpm, I still need to balance the carbs so I think this is the issue here)
    I have swapped the coils over but the same cylinder is the problem.

    Do you think the rings could be a bit stuck on one cylinder letting some compression through while its cold and then sealing better once warm?
    Or maybe a valve?
    I will be checking clearances tomorrow but thought I'd put it out there in case its a common one that I don't yet know about.

    Thanks in advance
     
  2. Gen

    Gen Well-Known Member

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    Sounds like a valve clearance problem (or the lack of) to me
     
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  3. ShaneP

    ShaneP Well-Known Member

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    How did you go? Did syncing the carbies help? Given the flat spot, I would think there's an issue with the carbies, still - if the intake and exhaust are modified, then that might be the reason for the flat spot. I'd guess the valves were ok? The rings could be an issue, you could go a bit of threebond engine conditioner down the cylinders.
     
  4. Martin Green

    Martin Green Active Member

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    Its a complete mystery. I have now cleaned the carbs, reset to factory settings. Checked the valve clearances and reset properly.
    The bloody thing is worse now.
    It starts on one cylinder with the choke fully open. If I gently turn the throttle speed screw I can get it to gather revs and the second cylinder fires up and sounds lovely. If I rev it even slightly too much it bogs and dies.

    Could I have an ignition issue?
    It feels as if the HT lead is cracked and only gives a spark when the revs are slightly higher. I have killed two sets of plugs already as if its struggling to loose the voltage properly.

    What do you think?
     
  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  6. Martin Green

    Martin Green Active Member

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  7. ShaneP

    ShaneP Well-Known Member

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    Air leak? Spray a bit of wd around the carbies and intake boots when running and see if it picks up revs. Make sure your vacuum line to the tap is good, and the tap isn't leaking fuel into the vacuum. What is happening to the spark plugs? Blackened is too much fuel, white is not enough. If you are using choke, then it seems like fuel shortage. Are you sure all the passages in the carby were clear? Swapping the coil showed it wasn't the coil or lead, maybe a bad wire on the loom/eco connectors?
     
  8. Martin Green

    Martin Green Active Member

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    Thanks for your response Shane.
    I have sprayed wd around and it made no difference. I did a dry and wet compression test and achieved around 125 in both cylinders. (fresh battery/throttle open) Its not great but should suffice.

    the spark in the right cylinder has no colouration at all and the left looks acceptable as far as colour is concerned.

    Once warm it runs but now i feel like it still only on one cylinder, if i open the throttle too quickly it just dies.
    It looks as if its blowing fuel out of the right pipe.
     
  9. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Are the primary leads correct?

    zzr.png
     
  10. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Sounds like the idle circut (not the jet) is blocked somewhere.
     
  11. ShaneP

    ShaneP Well-Known Member

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    Is it definitely fuel coming out the pipe? If so, the spark plug should be wet with fuel, too. That's a lot of fuel, I'd be looking at the air jets/passages or float level or vacuum valve of the tap.
     
  12. Martin Green

    Martin Green Active Member

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    So, I have cheated.

    I picked up a low mileage GPX250 and I'm going to do an engine swap. I know its geared a bit differently but hey, I have other bikes to do big miles on.
    This new bike has loads of good bits to swap over including a set of very trick stainless pipes that have a cool up sweep on them.
    It'll mean playing with the tail section a bit as it deletes the passenger pegs.
    The Gpx has a smaller 16" front wheel I believe so I cant do a fork swap unfortunately as the forks have been stiffened and are in better condition than the zzr ones I have.
    Maybe I'll just change the engine over a recoup some costs selling the other good bits.
     
  13. ShaneP

    ShaneP Well-Known Member

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    You try just a carby swap.
     
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  14. Martin Green

    Martin Green Active Member

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    Thanks Shane, that was my thought too.
    Its much newer so i'll look at the ignition components as well, but i'll start with just the carb.
    The gpx has been track prepared by some pro's so its a shame the forks don't fit. They are nicely set up.
     
  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Change 1 component at a time so u know which is the problem by trial and error
     
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  16. DannoXYZ

    DannoXYZ Well-Known Member

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    yup, sure sign deeper carb-restoration is needed. Most likely pilot circuit needs more cleaning for off-idle stumbles.

    1. measure all jets and replace them with OEM sizes. Many a carb has been drilled out by POs.

    2. Scrub all fuel-passages between jets and carb-venturi with scrub-brushes and solvent

    3. use piano/guitar wire to poke out lateral bleed-holes in emulsion-tube and pilot jet.

    4. ultrasonic soak carbs for days

    5. micro soda-blast all fuel-circuits

    6. re-assemble, replace all O-rings and seals, bench-sync, set float-levels, etc.

    Many expert mechanics have had to remove their carbs 4-5 times for ever deeper cleaning and refurb before their carbs ran like off showroom floor.

    I suggest you do this 1st time around with carbs from new
    bike as well. There's never enough time to do it right 1st time around. But there's always time to do it again!
     
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  17. DannoXYZ

    DannoXYZ Well-Known Member

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    Spray carb-cleaners no longer work due to removal of chlorinated compounds. Need to completely disassemble carbs down to every last component possible.

    [​IMG]

    Mechanically scrub out all petrol passages. Poke out all bleed-holes in emulsion-tube and pilot-jet with guitar wire of matching size (be extremely careful not to scratch off any brass). You'll notice it'll push out little dried-petrol plastic plug like grain of sand. This is extremely important components as they take over petrol-metering from idle-jets when you open throttle. And these being clogged is why bike falls flat on its face when you open throttle.
    [​IMG]

    Scrub out every surface-area petrol flows with scrub-brushes and solvents (I like PB-Blaster, 50/50 acetone/ATF mix).
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    When carbs have been restored to factory-fresh clean, bike will run like brand-new off showroom floor. Unless you buy brand-new carburetor from authorized Kawi dealer, most likely any carb you get will have sat for at least 6-months. Thus dried petrol inside has turned to plastic and will not dissolve again. Can only be removed by mechanical means. Good news is if you do full-restoration job immediately, you won't have to keep on pulling carbs for ever deeper cleaning.
     
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  18. DannoXYZ

    DannoXYZ Well-Known Member

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    Depending upon what was upgraded in those forks, you can just take upgraded innards out and swap into yours. Most likely just stiffer springs and heavier weight oil at higher level. Easier and faster job, 30-60min, because you don't have to remove entire front-end and re-fit brakes and wheels.

    See if it has Racetech Gold Valve Emulators. Those are some of best upgrades available for those forks.
     
  19. ShaneP

    ShaneP Well-Known Member

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    Ultrasonic cleaning of carbies works best at over 80°C: the varnish goes powdery an brushes off, the channels can be cleaned with carby cleaner and compressed air. Dry the carb thoroughly, make sure the carby cleaner flows through the circuits (and don't get it in your eyes!). Compressed air is good when cleaning carbies, other useful tools are fine wire from a multistrand copper wire or cable and heat - you can heat a jet and boil out some of the resin/varnish gunk.
     
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  20. Martin Green

    Martin Green Active Member

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    That is a fabulous reply and article, thanks so much for adding it. I will follow it religiously.
     
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