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Help Yamaha Zeal - hesitation below 6000rpm

Discussion in 'Yamaha 250cc In-Line 4's' started by boganracing, Nov 22, 2016.

  1. boganracing

    boganracing Member

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    hi all

    i have a 1999 model yamaha zeal and as of late it has had issues, it will go fine but after about 30mins of riding if i give it heaps it will then hesitate from idle up to 6000rpm then is fine all the way through the rev range, until it gets below 6000rpm again, in neutral it will idle and rev fine but when riding it will not, i have had carbs rebuilt less than 2000k ago and ive tried different coils and i have closed the plug gap a bit and its not as bad but still does it, has anyone got any suggestions?
     
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Have you adjusted the valve clearance's?
    Or might be float height/fuel level's, mixture adjustment
    Mixture's need to be set with the engine warm eg after a ride
     
  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Get the bike up to temp, stop and idle somewhere and ever so slowly creak the throttle open more and more. If you get lumpiness or hesitation to rev below a certain RPM then you know it's a carb sync problem. Other ways to tell include excess vibrations through the handlebars, lumpy idle.
     
  4. boganracing

    boganracing Member

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    Would the float levels and mixtures be out after only 2000k since rebuild? I took it in to get valve clearences checked but mechanic said since bike doesnt have 40000k on it yet its not due for it
     
  5. boganracing

    boganracing Member

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    So creak the throttle while in neutral or while riding?
     
  6. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    It depends how good the person doing the rebuilding is and whether they used new parts or just cleaned up what was there. As for valve clearances, is your bike a grey import (does it have an import compliance plate) ? What year is the bike and what is listed on the compliance plate? The mileage on imported bikes is often wound back.

    Also, valve checks/adjustments are due at minimum every 24,000 KM

    In neutral
     
  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    what was replaced on the carbs when they were rebuilt?
     
  8. boganracing

    boganracing Member

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    im pretty sure it is a grey import, prehaps il try a different mechanic

    as for what was replaced when carbs were done, i cant say for sure but as far as i know it was all the rubber parts and gaskets
     
  9. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK what you were describing could be caused by worn emulsion tubes and needles making it run rich and hesitate in the low RPM range

    Are you up to removing the carbs to have a looksee?

    It's not difficult to do and there's an abundance of helpful members here to give assistance wherever needed
     
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  10. boganracing

    boganracing Member

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    I wasnt to keen on pulling the carbs apart myself as i feel it will only end badly for me haha.
     
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  11. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Buy a set of JIS screwdrivers and work carefully, it's basically what we did... and to quote @maelstrom , you cannot butcher your way through rebuilding a carb.
     
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  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    here's a longish thread on needles and emulsion tubes, which may be causing the problems

    http://2fiftycc.com/index.php?threa...-tubes-fzr250-mikuni-bdst28-carurettors.9023/

    I don't want to leap to give a definitive diagnosis, but disassembly just to the point of being able to inspect them isn't a difficult procedure at all, and there's heaps of carb info on this site because so many of us have battled with them and we'll help you with any info.

    BTW I have a set of Zeal carbs which are in good condition, which have the worn needle jet (emulsion tube), so it happens to the zeals also

    Other elements which affect the carbs is fuel height, which you can check simply without any disassembly, probably a wise first step and should take about an hour at most

    http://2fiftycc.com/index.php?threads/questions-about-carburetors-yamaha-zeal-250-fzx-250.2141/
     
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  13. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    You can use posidrive screwdrivers on the JIS screws which are used on the carbs.

    Avoid using Phillips screwdrivers because you'll likely end up with several screws with damaged heads that need to be drilled to remove them.

    One of the good quality screwdriver handles with the interchangeable bits inside will have posidrive bits and should cost $20.

    I replaced all of the float bowl screws with good quality stainless allen bolts.

    In case you haven't guessed we're all about DIY on this site because so many mechanics won't work on grey market imports because of the difficulty in obtaining parts sometimes and it's much less expensive
     
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  14. boganracing

    boganracing Member

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    thanks for the advice, i will have a tinker on the weekend and report back...one more thing, would i be damaging anything riding it? as i said it only does it once warm and under hard acceleration normal riding it seems fine
     
  15. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    It could be but it'll take a bit longer to do the damage, luckily it's a 4 stroke and not a 2 stroke, a 4 stroke is a lot more forgiving
     
  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    If our theories about it running rich below 6000 RPM then the biggest downside will be poor fuel economy
     
  17. boganracing

    boganracing Member

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    I took it for a ride on Sunday and pulled up in an industrial estate and slowly reved it and it would hesitate/miss from about 4000rpm to about 5500rpm so would this indicate carb sync problem?
     
  18. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    It could well be an indicator. Do the handlebars vibrate a lot? 4 cylinder bikes should be smooth.

    You might also want to check the that the plug leads are securely attached to the plugs. They can pop off or come loose.
     
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  19. boganracing

    boganracing Member

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    i cant recall any vibration but then again i wasnt looking out for it....i changed the coil packs awhile ago because i thought they were the issue but apparently not because it still did it haha, fingers crossed it just the carbs out of sync, will put it in soon to get valve clearances and syncing done and fingers crossed it fixes it
     
  20. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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