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Bigfoot Engine "Misfires", Bouncing on Tire under Load

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  • #1

    Bigfoot Engine "Misfires", Bouncing on Tire under Load

    Hey there, I have a Bigfoot with a functioning clutch lever and a 29cc RC Chung Yang engine attached.

    Background:

    I recently installed a new Chung Yang head and piston. Broke in the motor and was hitting max RPMs. Took it out on the trail near my home yesterday and it stranded me.

    Issue:

    Went down a hill on it, let the engine die and started it back up. When I dropped the spindle on the tire it misfired, kicking the engine back up and dropping it back down on the tire jerking the ped back and forth until it stopped. Last time I had this I replaced the spark plug and it work fine again. Not the case with this.

    Work/Inspection Since Issue:

    I took the thing apart again and inspected the cylinder. There was a SLIGHT scratch along the side of the piston.

    I bolted the head back up adding washers and anti-seize since I wasn't using any on the head previously.

    I replaced the spark plug with a brand new NGK plug.

    I attempted to run it this morning and it misfired, sputtered, and bounced again.

    There's white smoke constantly coming from the exhaust pipe.

    The engine idles fine and even hits full RPMs -very responsive- while the spindle is above the wheel.

    Questions:

    What could it be? I hear misfires are usually spark issues. Is it worth getting a new magneto coil?

    Honestly just considering a new engine from DDM for $200 but I'd love to fix it if possible.

    Tags: None
  • #2
    Where did you apply antiseize? Hopefully not inside the engine. A slight scratch is fine, that’s not gonna be the issue. Also these coils never go bad so it’s not that. The most complicated mechanical component on these engines is the carb, so if everything else is mechanically sound, I’d put my bet on that. Also check to make sure your spark plug wire and/or kill switch wire isn’t grounding somewhere.

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    • #3
      Are you running a lock out? The clutch on a bigfoot is pretty much useless on RC style engines and will bounce up and down due to the increased hp. This could be your problem and I would suggest using a lock out.

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      • #4
        Originally posted by dsport View Post
        Where did you apply antiseize? Hopefully not inside the engine. A slight scratch is fine, that’s not gonna be the issue. Also these coils never go bad so it’s not that. The most complicated mechanical component on these engines is the carb, so if everything else is mechanically sound, I’d put my bet on that. Also check to make sure your spark plug wire and/or kill switch wire isn’t grounding somewhere.
        You're the best thanks for your response, that's a super solid checklist and you ended up being correct about the carb. Didn't apply anti-seize in the engine, just on the head bolts. I'm glad to hear that's not the issue. I really shouldn't have been taking it apart so much, glad to hear it's tougher than I've been treating it. Awesome to hear its not the coils, although a sketchy GoPed I bought for $150 a few weeks ago had it's cut with a knife lol.

        I leaned out the idle screw a bit and it fired up like a dream, topped out down the road.
        ​​​​​​

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        • #5
          Originally posted by monster2.0 View Post
          Are you running a lock out? The clutch on a bigfoot is pretty much useless on RC style engines and will bounce up and down due to the increased hp. This could be your problem and I would suggest using a lock out.
          I'm dreading a lockout but that may be inevitable for me. I love being able to keep it idling at stop signs and stop lights. Isn't there a spring system that will keep the spindle engaged with the tire but still allow you to raise it when you want to idle?

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          • #6
            There should be a spring on your bigfoot that keeps the engine down, pretty sure you can order them from DDM if your is missing.

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