Motor starting to miss

Discussion in 'Motorized Bicycle General Discussion' started by raneyd, May 21, 2008.

  1. raneyd

    raneyd Doug in Wyoming

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    I completed my bike build and have been really happy with the results. I have run about two gallons of gas through it and it is starting to misfire especially if I am going up a hill. I started this hobby as a way to learn something about motors. I would appreciate some help in what I should try first to fix this. I could take it to a local shop but would like to try to fix it myself first. Isn't it always more fun to take it to the shop after screwing it up yourself first. Any help would be greatly appreciated.

    Thanks.
     
  2. RedB66

    RedB66 New Member

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    What size/type of motor are you running?
     
  3. raneyd

    raneyd Doug in Wyoming

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    It looks to be the same as the one pictured on your bike (the traditional motor kit from China). I purchased it from Kings, it is the one they sell as an 80cc which as I read from posts here it closer to 67cc.

    Thanks.
     
  4. Jemma Hawtrey

    Jemma Hawtrey New Member

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    Have a look at the plug to see if the engine is running lean/rich - it could be running lean under load which may explain the misfire.

    If the mixture is ok then you should get a dry plug tip with a tan/brown colouration.

    Other problems could be to do with the ignition and also the petroil mix (if you are running a two stroke).

    hope that helps

    Jemma xx
     
  5. raneyd

    raneyd Doug in Wyoming

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    What ratio of oil to gas do you recommend?
     
  6. Ilikeabikea

    Ilikeabikea Moderator
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    After break in I run mine 30 to 1.............
     
  7. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    So uphill it "misses"....give me a slight more amount of info...does the engine go flat for power, or does it just "pop" a miss....???

    Indeed get a new NGK plug and a nice 7mm auto sp wire with 90° boot.

    Then use a good oil at 25:1 or 30:1, depending

    What needle slot are you using?

    Remember a 67 cc engine is not a torque monster. I think the compression ratio is really low, so again this limits torque - plus worst of all the power band is narrow and you ain't got gears to keep the power in the band.

    Also, you can check for intake tube leaks and match the intake and exhaust ports. The intake manifold is a notorious bad match to the port PLUS is has weld protrusion that you can clean up.
     
  8. deacon

    deacon minor bike philosopher

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    Sounds like they have you covered.

    The sounds coming from these engines can fool you but if it has been running good and is now missing I would vote ignition plug and wire.
     
  9. raneyd

    raneyd Doug in Wyoming

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    Thanks for the help, I ride on a pretty consistent route and it seems that your description of the "engine going flat for power" is a better description of what happens. I ride the same hills and have gotten used to a certain performance level and feel that I have fallen below that. I am embarassed to ask but what is a NGK sparkplug?

    What are the plug signs that the engine is running lean or rich?

    Thanks for taking the time to help me out.
     

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