Engine vibrations, not from mounting

Discussion in 'Motorized Bicycle General Discussion' started by fischer550, Apr 21, 2014.

  1. fischer550

    fischer550 Member

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    Yesterday I put a new CDI on my bike, one that I found on ebay rocket racing cdi. Worked great, rode it and engine did run a lot smoother and less vibration. Now today, for some reason it's vibrating much worse, and heres the iffy thing. When I pull in the clutch going to a stop, the engine revs up for a second, but does go back to normal idling. What could this be?
     
  2. fischer550

    fischer550 Member

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    and to add, i played with the idle screw and no matter what the engine would still always rev up when i pull in the clutch, so its not that the idle is too high.
     
  3. Greg58

    Greg58 Well-Known Member

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    Sounds like a air leak on the carb or the intake to cylinder, I would check everything I could for loosness for the vibration.
     
  4. 2door

    2door Moderator
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    Ditto: Your symptoms are consistant with an air (vacuum) leak. Most likely at the carburetor/intake manifold or the intake manifold gasket at the cylinder.
    You didn't say what carburetor you have. That might help us make some recommendations. If you can assure that there are no leaks at the intake system then you could be looking at a bad crankshaft seal either on the clutch or magneto side but check that intake area first.

    Tom

    Tom
     
  5. fischer550

    fischer550 Member

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    I have a stock NT carb, but I just ordered a new racing carb coming in the mail. I did discover a small head gasket leak, could this be the problem? I fixed the leak, now it only revs up a tiny bit, but the vibrations are still terrible.
     
  6. Greg58

    Greg58 Well-Known Member

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    Does it vibrate all the time or at a certain rpm? A lot of these engines hit a rpm range that give a lot of vibration, on one of my bikes its at 28 to 29 mph. On another it was 25. The type of tires help also, I changed from a 2.125 on the rear to a 1.95 and the vibration increased a good bit so I'm going back to the 2.125.
     
  7. mapbike

    mapbike Active Member

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    Ill agree it does sound like you have an air / vacuum leak, make sure the carb is pushed up tight on intake tube and for sure che k to be sure the gasket between intake and cylinder is good.

    I had one engine do the same thing and on mine it was the crank seal under mag rotor, hopefully your leak is a simple gasket and not the seal.

    Best wishes.
    Map
     

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