Blue wire to black wire nightmare

Discussion in '2-Stroke Engines' started by Fabian, Sep 8, 2009.

  1. Fabian

    Fabian Well-Known Member


    I've just joined the forum and wanted to repost my original post in here - should have done it in the first place.

    Hope there is someone who has gone through this nightmare and solved the problem.
    You can respond directly by email if you wish:

    Basically the engine ONLY runs when the blue wire is connected to the black wire.
    If i run blue wire to blue wire and black wire to black wire, the motor DOES NOT RUN AT ALL, but, when the sparkplug is removed from the cylinder head and resting on one of the cooling fins, it sparks just beautifully.
    I have tried 3 different sparkplugs with the same result.
    I have removed the magneto from the previous engine and installed it on the current engine and have also installed a brand new CDI unit but the problem is still the same.
    Only runs when blue wire is connected to black wire and it constantly misfires when it runs and has no power and doesn't want to idle.
    I've cleaned out the carby, cleaned the air filter and installed a new fuel filter just to be sure and disconnected the white kill switch wire but the problem still remains.

    I am going out of my head with frustration.
    During the day, and by chance, someone rode up my street with a Chinese 2-stroke motor on their bike and they had the blue wire connected to the blue wire, so i have no idea as to why my current setup does not run properly and fails to run at all with blue wire and black wires connected to each other.

    Your knowledge would greatly be appreciated.


  2. nadroj

    nadroj Member

    does it run perfect when you connect blue to black
  3. furament

    furament New Member

    did u flip the mag coil?
  4. Dilly Bar Rob

    Dilly Bar Rob Member

    Hello Fabian.

    Sounds like quite a predicament you have there. Electrical problems can be real headscratchers (I would know - I'm a low voltage electrician by trade...). Lets see what we can do for you.

    My first guess was magneto or CDI, but you swapped them for known good parts and still have the exact same problem. Good call on disconnecting the kill switch for troubleshooting.

    You say that when wired blue-blue & black-black you get a strong spark but the engine will not run? I would stop right there. Leave it hooked up like that and investigate further. It sounds like the ignition timing is way off. When you swapped the magneto did you swap just the "coils" or did you swap the "magnet" (round thing bolted to crank) as well? If you swapped just the coils take the magnet off (might have to take the coils back out) - there should be a "key" between it and the crank that ensures it only goes on one way and doesn't spin on the crank. If the key is missing (would not surprise me...) or sheared for some reason then that is your problem as that would throw the timing off. If it is there and everything looks ok then try replacing the magnet with one off of the engine that sourced the magneto - the one on it now may be machined wrong.

    If even that doesn't help then the groove in the crank that the key goes into may be machined in the wrong spot... Lets hope that isn't the problem though as that would be kind of hard to fix...
  5. Fabian

    Fabian Well-Known Member

    I thought of the magnet not being aligned correctly on the new engine but it is in the same position as the old engine.
    This is the replacement engine for the one that had the bottom end bearing problem.
    That engine ran perfectly so i used it as a guide to check the indexing of the magnet on the new engine.
    With blue connected to black the engine runs very poorly, makes no power, misfires and won't idle

    The old engine has the keyway facing just infront of the bolt/screw that sits just ahead of the rear cooling fins on the barrel and the new engine has the magnet aligned exactly the same, although i have not taken the nut and spring washer off the crankshaft to see if the magnet has been installed without a woodruff key and reversed 180 degrees.

    What is the effect of radially rotating the magnet 180 degrees on the crankshaft (would the ac waveform be the same) and also inverting the magnet on the crankshaft so that the spring washer and nut clamp down on the opposite side of the magnet (would the ac waveform be the same in this circumstance).

    I am at a total loss to even understand what is going on, since the other engine ran perfectly.
  6. furament

    furament New Member

    should be the same ether sid of the mag well and all 4 magenrts are in the same spot but what i wus thinking was if maby u got the mag coil upside down and bacwards? i thinc its blue wire down wite wire up ground on top?
  7. furament

    furament New Member

    and ya if its instaled without the key to index it your timming would with out reference
  8. Fabian

    Fabian Well-Known Member

    I have not installed the magnet or removed the magnet from the engine.
    I can just see the keyway and with engine at top dead centre the keyway is at about the 1 oclock position and the magnet keyway lines up with where the crankshaft keyway would be on the old engine.
    At top dead centre, the old engine and the new engine had the magnet in exactly the same position at top dead centre.

    I'll try and attach a pic.
  9. Fabian

    Fabian Well-Known Member

    Photos attached of magneto, magnet and blue wire connected to black wire

    This problem is driving me to the brink of despair

    Attached Files:

  10. Dilly Bar Rob

    Dilly Bar Rob Member

    Is it possible to "flip" the magnet front to back and put it on the other way? Maybe it's on backwards... Not quite sure if north-south polarity being opposite would make a difference but it might be worth a shot seeing that you already tried everything else. Also try to swap the magnet from the other engine, be sure that you have the same side facing "out".
  11. Fabian

    Fabian Well-Known Member

    Pic attached of magnet orientation when flipped over and located on crankshaft keyway with piston at top dead centre.
    Compare this pic to the other pic of magnet in the original position when located on the crankshaft keyway.

    I've yet to flip the magnet over on the new motor to see if this solves the problem of a non running motor when blue wires and black wires are connected to each other.

    I'm out of ideas if this does not solve the problem.


    Attached Files:

  12. Fabian

    Fabian Well-Known Member


    I've flipped the magnet over and the motor runs with blue wire to blue wire and black wire to black wire, but still makes no power, misfires and won't idle - feels like it runs worse than before.
    It won't run at all with black wire connected to blue wire and black wire connected to blue wire.
    I even connected white wire to blue wire and blue wire to black wire but it did not run at all.
    After that the motor does not run with wires connected either way.
    With sparkplug removed from cylinder and resting on cylinder head, the spark is weak and intermittent.

    For gods sake, will someone give an answer to this god d****d son of a B****H, piece of garbage engine.

    I can't take any more of this frustration, considering i've tried ever god d****d possible combination and nothing works.

    Last edited by a moderator: Sep 9, 2009
  13. Fabian

    Fabian Well-Known Member

    This is driving me insane

    I've flipped the magnet back over to the original side; the way it was installed on the engine from the factory.

    The engine runs the same as before, with blue wire connected to black wire and black wire to blue wire, but just as before, it misfires, has no power and won't idle.

    Every single possible combination of options has been tried, unless there is one that i've missed.

    Why did the previous engines electrics work perfectly and even with the electrics from the old motor installed on the new motor does the new motor not want to run properly.

    It defies understanding

  14. furament

    furament New Member

    flip it over so it runs blu to blu dry your conectors with a heat gun and see if it helps the lack of power could fule but some times u just get a dog
  15. srdavo

    srdavo Active Member

    Just a thought.... if it starts & runs, it doesn't sound to me like an electrical problem.
    Double check your carb:
    the needle & jet
    And the needle valve & float assembly.
  16. Fabian

    Fabian Well-Known Member


    I put the bike on my car trailer and took it down to the shop where i purchased the engine.
    For 2 hours their shop mechanic tried everything - there was much head shaking, swearing and cussing from the shop mechanic after he admitted defeat - the engine missing problem was unsolveable even after every single component was changed over for brand new components.

    In the end they gave me another engine.

    After installing the 2nd, replacement engine, it fired up on the first go with the black wire connected to the black wire and the blue wire connected to the blue wire; the engine idled beautifully and runs like a dream.



    If anyone ever has a situation where the engine only runs with the blue wire connected to the black wire and the black wire connected to the blue wire, PLEASE, do not even attempt to try and work out what the problem is - JUST RETURN THE ENGINE AND ASK FOR A REPLACEMENT.

  17. Al.Fisherman

    Al.Fisherman Active Member

    I've been watching this thread wondering what in the electrical system could cause that problem. After reading what tests you went through I've come to the conclusion.....It couldn't of been a electrical problem, had to be something else, if ALL the electrical parts were either disconnected (kill switch) or changed out with known good parts, it had to be something else. The whole electrical system is such a simple system. I sure would like to know what it was causing the problem... An inquiring mind wants to know.
  18. Fabian

    Fabian Well-Known Member

    Hi Al.Fisherman

    As much as i don't want to say it - it can't be something else other than electrical because the carburettor has not been changed.
    After installing the original carburettor on the new engine, it fired on the first go and with the wires connected, blue to blue and black to black.

    The carburettor could not be the problem as i rebuilt the thing just to be sure, when trying to sort out the what was going on - carburettor was clean as a whistle upon disassembly.
    Just riding the pushbike, it would have been immediately evident to you that it was an electrical problem - carburation does not miss so instantainiously and so agressively.
    The shop mechanic knew straight away that it was an electrical problem.

    YES, i want to know what was going on too - don't like to be defeated by something so seemingly simple.
    After 2 days of sheer stress, you no longer have an inquiring mind, let me tell you.

    The worst thing to compound frustration is when you have a completed a course in Certificate II electronics and cleary understand that the ignition is a simple modular system - the simplest method is to keep replacing components till the problem is found, then replace the suspect part to verify that the problem reoccurs - at least it should be simple!

    I've solved some interesting electrical problems on cars but nothing like this Chinese engine has EVER brought me so close to using the 20 pond sledge hammer.

  19. Al.Fisherman

    Al.Fisherman Active Member

    This right here says that it was not an electrical problem...something else ...yes, but not electrical. That is as far as the individual components are concerned.
  20. Fabian

    Fabian Well-Known Member

    Unfortunately that is a bad diagnosis.

    The original carburettor on the engine ran perfectly
    The replacement engine had the original carby installed on it and it failed to run properly - the original carburettor was disassembled, inspected, found to be perfectly clean, lightly blown down with compressed air and reassembled.
    The engine still did not run properly.
    The second replacement engine had the original carburettor installed and it ran perfectly.

    This verifies that the carburettor can be eliminated as a source of the problem and the nature of the problem was totally consistant with electrical issues.

    Secondly - the 1st replacement engine was run with the fuel tap in the "on" position then turned to the "off" position whilst running under some semblence of load until the carburettor bown ran out of fuel.
    The engine continued missing with full fuel flow through to restricted fuel flow through to running out of fuel.

    The engine was missing consistantly and repeatedly till the carburettor bown was empty.
    There was no change in the nature of the engine.
    If the carburettor was flooding, then the engine would have run better towards the end of fuel flow to the main jet.
    If the carburettor was running lean, it would have lost power (the power that it had) and the misfire wouls have increased and the engine would have run better with the choke slowly closed off.

    This process of diagnosing a carburettor problem has been well and truely tested in the process of eliminating potential sources other than electrical.

    The Carburettor was not the problem and the operation of the engine made it clear that the electrics were involved