Engine Trouble Brand new bike worked for about 30 minutes and broke down.

Discussion in '2-Stroke Engines' started by Snowpoison, Jul 27, 2014.

  1. Snowpoison

    Snowpoison New Member

    Ok so I just finished putting a 66cc engine on my bike. Everything was running perfectly. I rode like twice around the block and then let my brother have a turn. So he rode up the street and came back with his arm all cut up. Apparently he pulled the front break instead of the clutch and went over the handle bars. I don't know if that has anything to do with the engine not working because it was running fine after that. So I'm riding, I'm about two miles away from my house (after the accident I might add) and things are going good. Then I turn around to come back and nothing. The engine just died. It didn't sputter or anything, just shut off and wouldn't start back up again. So me and my brother decided we would try to figure it out. We put a inline spark checker on and got nothing. So we have it narrowed down to spark, but we swapped plugs, still nothing. We swapped coils, still nothing. So I guess it has to be something with the magneto, but after removing the cover we can't see anything wrong. No water (the engine hasn't even been near water) No obvious damage. The wiring has been checked and double checked and we can't find anything wrong with it. We're pretty much stumped and that's why I'm turning to a forum! Thanks in advance!

  2. john doe

    john doe New Member

    do you have a multimeter? If so, check the testing resistance between engine/magneto wires, between killswitch wires, and from engine to switch. If the killswitch reads an infinity symbol without the switch open, that might be the problem. I have the testing resistances for everything else written down somewhere, i'll dig in my toolbox later.

    Aother way to test for a bad kill is to totally remove those wires and see if the bike fires. If it does so just fine, that was it.

    tl;dr first guess is bad killswitch. you've ruled out wrong wiring order since it was running before. Bad magneto is possible but for some reason doubtful.

    idk, just my 2 cents. i'm no expert.
  3. KCvale

    KCvale Motorized Bicycle Vendor

    That is exactly why you don't want 2 levers on the same side of the handlebars, especially in an emergency situation.

    Do yourself a favor and get a self-adjusting dual pull brake lever from SickBikeParts for $12 and pull your 2 stock brake levers off.

    My rule of thumb for handlebars is no more than than 2 levers and 2 twist controls on the handlebars.

    Do you still have a front derailleur?
    I just yank the whole system off and put a rotary shifter for the rear on the left with the clutch, the throttle and dual pull brake on the right.

    You don't get as many operator errors that way.
    The first and easiest check for igntion problems is just ohm the black wire to the CDI and a head bolt.

    This isthe spark plugs ground, it should read a dead short, if not check the ground tab that solders onto the magnet on the magneto coil.

    With the CDI disconnected your magneto black and blue wire should ohm out to ~325 ohms.

    You can also ohm your disconnected CDI.
    Put the meters + lead to the CDI's black ground wire, the - to the spark plug connection in the plug wire.
    You should get ~ 6.92K ohms.
  4. Snowpoison

    Snowpoison New Member

    Ok so I disconnected the wire coming from the kill switch, still no luck. It doesn't even try to start.
  5. Snowpoison

    Snowpoison New Member

    *update* I swapped the magneto coil from an old 49cc bike that hasn't been run in about a year. Just tested it and still nothing.
  6. john doe

    john doe New Member

    No spark after replacing the magneto? or is there a spark but the engine won't fire?
  7. HeadSmess

    HeadSmess Well-Known Member

    pulled the plug, and checked it on the head? try a different plug altogether too.

    checked the engine case and magneto for clean contact area? thatll kill it. as KCvale said...black to the engine casing AND THE HEAD ITSELF should be a short, 0 ohms, the indicator light glows, the buzzer will beep, or anything else that indicates continuity. anything else and its an earth issue.
    (also agree about keeping the levers to a minimum...if you lend it to ANYONE, or sell, or are liable for anyone elses sheer stupidity in any way...)
    erm.... sudden death is always electrical... thinking, thinking...

    plug. my money is on the plug. everything else has been suggested, that i can think of right at the moment but ill have another idea in about fifteen seconds.


    nope. nothing yet.


    BOTH wires from the killswitch disconnected? not that that makes any difference :jester:

    forget that. you did the plug too. oh dear...

    continuity to the head is about the last possible cause, if you have tried swapping everything else... but why? no, this dont make sense.

    remove the spark plug and verify it has no spark. i have a feeling were all chasing wild geese now. an inline spark checker? a WHA?

    you hold the plug against the head or engine case, thats definite. dont trust any electrical doo dad!

    last one. the key has sheared, everything looks a-ok, but in reality, the magnet simply is spinning ON the shaft, not WITH the shaft...
    Last edited: Jul 28, 2014
  8. Fabian

    Fabian Well-Known Member

    :iagree: but you still need the left hand side brake lever to operate the clutch.
  9. Snowpoison

    Snowpoison New Member

    Ok so quick update! Sorry it took so long but I was on vacation the last couple of weeks. However, I bought a new magneto and an ngk spark plug. Put both of the parts on and it fired right up. I haven't had the chance to ride it much, but it worked great when i rode around the block. Thanks to all that helped, or gave advice! Cheers chums!
  10. KCvale

    KCvale Motorized Bicycle Vendor

    Just out of curiosity...
    Did you ohm out the magneto to prove it was bad?

    When you put the new magneto on was it really hard get the blots in because of the pull from the magnet?

    Believe it or not magnets do go bad, especially poorly made ones.
    If it was easy to mount the new mag don't expect it to run worth a crap because it is that spinning magnet that generates your spark and a weak magnet will make a weak spark until it won't make a spark at all.
  11. Snowpoison

    Snowpoison New Member

    Yes, the old one was definitely bad. And yes the magnet pulled hard on the new magneto. Thanks anyway :D
  12. KCvale

    KCvale Motorized Bicycle Vendor

    Good show ;-}