66/80cc Grubee High RPM Engine Cutout

Discussion in 'Motorized Bicycle Trouble Shooting' started by Maskot, Aug 11, 2016.

  1. Maskot

    Maskot New Member

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    Right as the engine starts to vibrate every nut loose, it cuts off and revs down to idle then after 2-3 seconds the power comes back.

    Fuel flow is good, spark plug is black :p, don't know jet size, probably too big, stock everything, NT carb, 1:35~40 fuel mix, 89 octane pure gasoline, does the same thing when moving or not.

    I think it's either the spark or the exhaust.

    If a thread already exists for this, please lock and post a link to it, thanks.
     
    #1 Maskot, Aug 11, 2016
    Last edited: Aug 11, 2016
  2. Chaz

    Chaz Well-Known Member

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    Two quick thoughts. Maybe vibration is foaming the fuel in the carb bowl. Possibly vibration is irritating some iffy electrical connection, particularly the magneto connection.
     
  3. crassius

    crassius Well-Known Member

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    fuel foaming in carb - something loose or sometimes happens with long, offset, intake
     
  4. Maskot

    Maskot New Member

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    I'm convinced it's fuel foaming, I have the engine mounted to the frame on dampers that allow it to rock side to side and prevents vibrations. I'm going to take those out, lock the thread bolts into the engine and tighten the mounts down with lock washers nice and tight. If this doesn't work, I think I'll try to make a custom shock mount for the carb to the frame and use rubber tubing to bridge the small gap to the engine intake.
     
  5. Chaz

    Chaz Well-Known Member

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    Yeah, ditch those dampers and see how she goes. Sounds like you gotta whole lotta shakin goin on. Hope that does it for you. Let us know.

    I have an older motor and it vibrates but smooths out at my higher cruising rpm.
     
  6. sboricic123

    sboricic123 Member

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    #6 sboricic123, Aug 12, 2016
    Last edited: Aug 12, 2016
  7. Maskot

    Maskot New Member

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    After the hard mount, I realized why I put the shock mounts in, All of the capillaries in my hands are shredded. It did fix the problem however and I'm happy for that.
     
  8. Chaz

    Chaz Well-Known Member

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    Glad to hear you got it sorted but too bad about the bad vibes. Maybe time to get one of the new balanced engines. Also you could try banging some fishing weights into the handlebars to reduce it somewhat. I haven't done this but I hear it helps. Best to research for options.
     
  9. crassius

    crassius Well-Known Member

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    sometimes moving the rear mount up or down just a 1/4inch and front mount the other way to keep it tight will stop some of the vibration
     

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