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Help Jerky when I slow to very low rpm - ZXR250

Discussion in 'Kawasaki 250cc In-line 4's' started by Rose, Dec 10, 2014.

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  1. Rose

    Rose Active Member

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    Hey guys,
    this is a bit difficult to describe so i hope you can understand what i am trying to say.

    My bike (ZXR250C 1992) has always since i got it, been a bit jerky when I slow down to very low rpms, about 2-4rpm, and try to steadily move at the low rpm.
    but it is only jerky when i try to stay going slow in the 2-4rpm range so i will most likely be in 1st gear.
    So for example, this occurs when i am in very slow, start stop, moving traffic.

    Other than this the bike runs perfectly and is very smooth and not jerky when i accelerate or decelerate through the 2-4rpm range, it is also very smooth when i accelerate, decelerate or sit at any other rpm.

    its almost like the throttle is at a point where is doesn't know if its on or off, so jerks between the two.

    The only reason i have not addressed this sooner is because i hardly ever find myself in traffic that is this slow moving because i just lane split, and did not find it to be a problem.

    Recently i have moved and am finding myself in more slow moving traffic and i also just installed a new aftermarket muffler :D

    After installing the new muffler, i found the bike runs a lot smoother but is now slightly more jerky in this situation.

    thus it had become an irritating problem.

    What do you think could be the cause?
    how do i fix it?
    and how much do you think this will cost me to fix?

    thanks,
    Rose
     
    Rose, Dec 10, 2014
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  2. Murdo

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

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    Could be the fuel mixture is a bit lean. Try adjusting the mixture screws out half a turn and see if this improves it.
     
    Murdo, Dec 10, 2014
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  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Check your chain tension as well, to make sure it's not slapping around everywhere
     
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    Linkin, Dec 10, 2014
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  4. Willrcr15

    Willrcr15 Well-Known Member

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    Check the cush drive isn't sloppy in the rear hub.
    Could be all of a few things combined.
    Check the chain for tight spots, may be stretched.
     
    Willrcr15, Dec 10, 2014
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  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Dec 10, 2014
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  6. The Wizard

    The Wizard Well-Known Member

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    I get the exact same thing. It's normally as I'm trying to go slow over speed bumps. It's like your gently chopping the throttle on and off. I just assumed a mixture of chain slack/wear and jetting. I usually just use some clutch as i don't hit many speed bumps
     
    The Wizard, Dec 10, 2014
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  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    One other thing to check is the Cush drive behind the rear sprocket - if it has too much play it feels like this. My Ninja is terrible for it. New cush drive ASAP
     
    Linkin, Dec 10, 2014
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  8. Rose

    Rose Active Member

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    Chain had 14mm slack so i tightened it to 7mm, and checked for tight spots, sprockets etc. and that helped it very slightly but its still happening. I will have a look at the crush drive sometime over the week.
    where could i get another crush drive sent to New Zealand? could anyone put up a link? I'm can't find any specific for the zxr 250

    I have a feeling its more that the fuel is running a bit lean, because it feels as though when its jumpy its that its not getting enough fuel or that its only getting little bits at a time.

    cheers for the help,
    Rose
     
    Rose, Dec 11, 2014
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  9. Willrcr15

    Willrcr15 Well-Known Member

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    Did you roll the chain along & check for tight & loose spots throughout the whole length, I know it's the spec but 7mm isn't much slack as long as it's 7mm on the tightest part of the chain.
    Get new genuine cush drive parts, they'll fit perfectly & be of the right rubber, should be a tight fit initially, worth the extra money.
    It'll feel beautiful when you've done it if the old ones are worn out & sloppy.
     
    Willrcr15, Dec 11, 2014
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  10. Murdo

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

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    If you think it is lean fueling, try putting the choke half on when it does it. This will tell if it is lean.
     
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    Murdo, Dec 11, 2014
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  11. Rose

    Rose Active Member

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    will give this a go
     
    Rose, Dec 11, 2014
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  12. Mclaren

    Mclaren Well-Known Member Contributing Member

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    7mm seems tight most bikes u want 20-25mm over movement
     
    Mclaren, Dec 11, 2014
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  13. TechHeadFred

    TechHeadFred Well-Known Member

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    Am I the only one who finds "Too tight: more than 15 mm" and "Too loose: less than 7 mm" illogical?

    @Mclaren - The chain slack here is measured with the bike on the side stand. Most settings I have seen are for the bike on a centre stand or with the rear wheel off the ground.
     
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    TechHeadFred, Dec 11, 2014
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  14. Mclaren

    Mclaren Well-Known Member Contributing Member

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    If wheel off ground no tension on chain and changes when weight on suspension then rider u will find it will tighten even further
     
    Mclaren, Dec 11, 2014
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  15. Mclaren

    Mclaren Well-Known Member Contributing Member

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    This is how I measure tension image.jpg
     
    Mclaren, Dec 11, 2014
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  16. Mclaren

    Mclaren Well-Known Member Contributing Member

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    7mm wouldn't cover chain thickness
     
    Mclaren, Dec 11, 2014
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  17. TechHeadFred

    TechHeadFred Well-Known Member

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    It does seem quite low.
     
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    TechHeadFred, Dec 11, 2014
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  18. TechHeadFred

    TechHeadFred Well-Known Member

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    I agree that if checking on the side stand the tension would be higher from the weight of the bike on the swingarm.

    The chain would therefore have less slack.

    This is from my Haynes CB250RS workshop manual:

    [​IMG]

    This is for a 34 year old bike though.
    Perhaps the method of checking chain tension has changed over the years?
     
    TechHeadFred, Dec 11, 2014
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  19. Rose

    Rose Active Member

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    I did the measurements with it on its side stand, but I can check what the measurements are on a rear paddock stand to see if it still fits these specifications.


    I saw that too had to read it about 10 times just to confirm that they must have made a mistake haha.
     
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    Rose, Dec 11, 2014
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  20. TechHeadFred

    TechHeadFred Well-Known Member

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    Glad it wasn't just me then!

    I'd say you're likely to have about 15-25 mm play on a paddock stand at a guess.
     
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    TechHeadFred, Dec 11, 2014
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