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Vibration between 3k-4k rpms

Discussion in '1st & 2nd Generation 1983-1989' started by slowbird, Apr 28, 2011.

  1. slowbird

    slowbird Member

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    I've had this problem with my 2nd gen since I bought it and I'm unsure what it could be.

    At around 3000 rpms and up to around 4000 rpms the bike has some vibration...enough that it's bothersome and almost foot numbing....but not crazy or dangerous.

    I've had the following done to my bike:

    -valve adjustments (many)
    -carb synchs (many)
    -New tires
    -New chain
    -New rear sprocket

    ....and it's still there.

    I can easily shift gears to keep the rpms under or over that vibration range so it's making me rule out wheel bearings.
     
    slowbird, Apr 28, 2011


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  2. donald branscom

    donald branscom New Member

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    Is it a vibration at 3,000 RPM-4,000 RPM while riding, or just sitting still?

    If you are riding and you pull in the clutch does it stop?

    Will it make the vibration while parked, and just revving it up?
     
    donald branscom, Apr 28, 2011


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  3. slowbird

    slowbird Member

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    I've only noticed it while riding.

    Yes it does. Pulling in the clutch kills the vibration.

    Dunnoh. I'll have to check that and get back to you.
     
    slowbird, Apr 28, 2011


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  4. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    My V4 used to have a "vibration" around 5500-6500 RPM. The motor just didn't feel good and smooth in that range. Footnumbing just like you described. I had to keep the RPM's low to be smooth and would sacrifice the power I needed pulling through the corners.

    Once I got my carb jetting right, it smoothed right out and I can run at 6000 all day long if I want to.
     
    tinkerinWstuff, Apr 28, 2011


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  5. slowbird

    slowbird Member

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    The bike has had the same vibration all through the time I've owned the bike.

    From the moment I purchased it and it ran fine...to when I was running rich and missing....and even now after replacing all the jets.

    No difference what-so-ever
     
    slowbird, Apr 28, 2011


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  6. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    Have you done an exhaust gas analysis yet to see if you are burning at 14:1 or so?
     
    tinkerinWstuff, Apr 28, 2011


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  7. slowbird

    slowbird Member

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    No. I am having trouble finding someone who can do one (or an affordable gas analyzer that I can buy) that doesn't involve welding a bung into the exhaust.
     
    slowbird, Apr 28, 2011


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  8. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    local shop should be able to do a simple dyno run for around $60. They would check idle, cruise RPM (where you are having issue), and wide open throttle. Then you'll know exactly what you're dealing with and can make your own informed adjustments accordingly. Reading plugs only goes so far and some will say it's even harder since lead was removed from fuel.


    Motorcycle Dyno Owners List

    Who knows what your problem is. All I do know is; I had the same symptoms until my jetting was adjusted right, you've been dealing with carb issues recently, and you don't know exactly what your mixture ratio is.
     
    tinkerinWstuff, Apr 28, 2011


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  9. slowbird

    slowbird Member

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    I am planning on having a local dyno check the A/F....I just need to find a shop that can do it without welding an O2 bung into the exhaust.
     
    slowbird, Apr 28, 2011


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  10. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    I know the local shops to me just stick a probe down inside the can.

    Don't forget the PAIR system will make the AF read extremely lean at idle. When I run, I pinch off the fresh air supply tubes to the PAIR valve in order to get an accurate reading at the tail pipe.

    [​IMG]
     
    Last edited: Apr 29, 2011
    tinkerinWstuff, Apr 29, 2011


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  11. slowbird

    slowbird Member

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    I have a PAIR valve on my bike?

    Where is this line I need to pinch?
     
    slowbird, Apr 29, 2011


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  12. Hawkrider

    Hawkrider New Member

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    No, there's no PAIR on this bike. PAIR didn't come out until '87 or '88 on the I4's.
     
    Hawkrider, Apr 30, 2011


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  13. commrad

    commrad New Member

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    I'm with tink on this one, my little 500 had a vibration in the middle of the revs. I never really paid the rpm much attention but it went away and the engine runs quieter, cooler and smoother after doing nothing but shimming the needles up a little.

    I read some where that they were set from the factory to lean out in the cruise range for emissions reasons.
     
    commrad, Apr 30, 2011


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  14. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    sorry, maybe there is no PAIR on that year.
     
    tinkerinWstuff, Apr 30, 2011


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  15. slowbird

    slowbird Member

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    Thanks for clearing that up.

    Thanks! I'll toss on my Yosh and get everything sorted before taking it to a Dyno so we can all figure out what the A/F is at.

    No apologies. I appreciate the info you have given me....I wouldn't have given this a thought.

    One more excuse to take it to get the A/F checked. Thanks Tink.
     
    slowbird, Apr 30, 2011


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