2nd bad magnedo and cdi in a week

Discussion in 'Electrical' started by joey d, Feb 1, 2010.

  1. joey d

    joey d Member

    last week I went on a ride and my bike died peddled it home discovered I had no continuity between the black and the blue wire on both the cdi and the magneto so I believe the magneto went and fried the cdi in the process. all wires were soldered shrink rapped and taped no moisture in the magneto because it was sealed properly.
    blue to blue
    black to black
    kill between blue and black

    figured the thin wire on the magneto coil broke from excessive vibration. I was at wot and moving.

    I replaced the cdi and the magneto. ran great again. put on a expansion chamber exhaust and an auto chain tensioner. took it on a 20mile ride. It ran great.
    3 days later I take it for another ride and it ran like **** bogging stuttering and dieing at stop signs. Then it died completely.

    I peddled my bike home again and now I have no continuity between the black and blue on the cdi and the magneto again. what is going on I never had this problem before with any of my other builds. I also never had a build that went this fast before When running right I'm getting up to 38mph. but I keep killing the electronics.
    any suggestions would be appreciated.

  2. Dilly Bar Rob

    Dilly Bar Rob Member

    Maybe your kill switch is shorting out intermittently?

    I don't know what the cdi unit should measure (if you can even measure it), the magneto coil should measure something, probably in the range of 10s to 100s of ohms (the exact value should be on here somewhere).

    I find it hard to believe that you killed 2 cdi's & 2 coils in such a short period of time, something else must be going on...
  3. joey d

    joey d Member

    I have tried disconnecting the kill switch. just took a better look at the first magneto. It had a brake where the thin wire coming off the coil is soldered to the metal bar (aka ground). I resoldered the connection and now am getting some readings. These measurements have been done on a work bench.

    blue to white=342 ohms
    white to metal plate(black)=2.5 ohms
    blue to metal plate(black)=345ohms

    screw and blue open
    screw and black 6.82k ohms
    blue and black 244.5k ohms

    I haven't gotten to see if the other magneto has the same problem. I have to check if the little coil wire soldered to the plate is broken but That is what I suspect. being the same symptoms with the open black.

    My question has this been a problem for anyone else out there. If you have a bad magneto laying around that just quit (not due to water damage) please look at this wire going to the plate and tell me if it is broken.

    thanks joey d
  4. AussieSteve

    AussieSteve Active Member

    Your kill switch should not be between the blue and black wires. That will fry magneto coils.
    The kill switch should be between the black and white wires. This is a higher impedance, more loosely coupled coil that can handle a short. The blue/black coil can't.
    If you really don't want to use the white wire, for some reason, use a normally closed PB switch on the blue wire for a kill switch, to open the circuit. (It's a bit harder to find a suitable normally closed switch, though.)

    ... Steve
  5. Al.Fisherman

    Al.Fisherman Active Member

    Steve I'm with you. Either between the black (ground) and white (hot), or one wire from kill switch to ground on bike (assuming the engine is not insulated) and the other to the white wire. On ALL instillations I remove the stock wires and solder new wires (16 or 18G) that will reach my CDI.
    Last edited: Feb 2, 2010
  6. joey d

    joey d Member

    why does everything I have read keep saying to just cap off the white wire? This is very confusing. Also I have hooked up my friends bike the same way. He rides his 35milles to work and back every day no problems. mine I haven't been able to make it 3 rides without having the magneto coil lose continuity between the blue and ground.

    I am beginning it is vibration related because there is no burning smell just a broken wire.
  7. AussieSteve

    AussieSteve Active Member

    Because you're reading the wrong posts. There is a lot of misinformation on this site, on many issues.
    There are also many posts saying to use the white wire for lighting.
    The white wire was intended for the purpose of connecting a kill switch. Some people think that they know more than the designer. They don't. Just stick to the recommended wiring and you shouldn't have any problems.
    This subject comes up every week or two.

    ... Steve


    Attached Files:

  8. joey d

    joey d Member

    thanks I better rewire my friends before his brakes too. thing is he has been riding his 30miles each way to and from work for about a month now no electrical problems wired kill between blue and black. mine lasts a couple days.
  9. Al.Fisherman

    Al.Fisherman Active Member

    Right out of the book.

    I run both wires to the CDI and connect one to the WHITE (Hot) and the other to the BLACK (Ground). I also have hooked the kill switch wires to the Blue and Black wires on the CDI without issues. I don't like tucking one wire under the handle and prefer a good solid ground connection. Like I said before I redo all the wires (16 or 18ga) from the engine, that way I have connections at the CDI and if a problem shows up I have isolated where the problem can be.

    Attached Files:

    Last edited: Feb 3, 2010
  10. joey d

    joey d Member


    I took a look at the 2nd magneto and It was the same problem. The thin coil wire was broken between where it comes through the plastic and the solider. I put some more solider on them both so now I have a spare. As for the cdi I was wrong about blowing them They both seem to be working. I am going to hook up my kill to the white and ground/black and hopefully I wont have this problem again. I still think it could have been vibration so I am gonna put a drop of epoxy on the wire too for reinforcement.
  11. Al.Fisherman

    Al.Fisherman Active Member

    When I get the wires straight I take a little RTV and seal the hole where the wires come out of the nylon bushing. This will keeps the wires from moving.
  12. cigron

    cigron Member

    I had the same problem. It would run great for while then miss and ran very bad
    and then some times it would stop.to make A long story short I put A ground strap
    on it thet I got from A auto parts store.
  13. joey d

    joey d Member

    weather I am burning or breaking the thin coil wire just between the the coil and the solider point, it only happens when I am going wot at full rpms. this would be when the magneto is producing the most electricity. I just don't know why it has been happening.

    1 If it was because of the kill switch being between the blue and black why isn't my friends bike having this problem?
    2 It wasn't moisture because I have it sealed up good with silicone.
    3 vibration? I don't think so It isn't to bad especially with my auto chain tentioner.
    4 Is the magneto just producing more electricity then that thin wire can handle when I am doing top speed, pushing those rpms? (possible?)

    I don't know what other reason would this happen?
  14. AussieSteve

    AussieSteve Active Member

    That's where you would expect it to go open-circuit from a short-circuit, (ie kill switch). It's the one spot on the coil where the wire isn't firmly touching other wire etc, allowing it to reach a higher temperature. Possibly, using the blue/black combo for the kill switch, you're weakening the wire at that point due to the high current flow during the short-circuit while the motor stops turning.
    Then, it could actually fail at any time.
    I re-iterate, for the last time, don't use the blue wire for your kill switch. The current flowing through this wire is much higher than that flowing through the white, while the kill switch is depressed.

    This isn't a common problem, especially not twice in one week. Either you're getting bad parts or you're doing something wrong. (Not pulling on the wires or anything like that?) Otherwise, the one thing that stands out is your use of the blue wire from the ignition winding to short the magneto/CDI and kill the engine.

    ... Steve
    Last edited: Feb 4, 2010
  15. joey d

    joey d Member

    thanks I am going to run from now on with the white and black as kill and see what happens. I have had the same problem with magnetos from 2 different suppliers. so I its not the magnetos them selves. Ill keep in touch and (keep your fingers crossed) be able to say I am having no problems.
    thanks everyone
  16. AussieSteve

    AussieSteve Active Member

    Hopefully that will cure the problem.
    I can't think of anything else.

    ... Steve
  17. dinoseer

    dinoseer New Member

    This is what might have happened to my Flying Horse Motor. Ran great for 2 days and now the Magneto Coil is dead. I bet it is that little wire rattled loose. Going to look first thing in the am...
  18. dinoseer

    dinoseer New Member

    Found 2 Issues with Magneto on 66cc Flying Horse Magneto

    I took the Magneto Coil Loop out this morning and found that indeed, that little tiny copper wire soldered to the Top Arm of the Magneto Coil had broken. Also found that the White Wire had damaged insulation, allowing the wire to touch the case inside. I will post photos later of the whole process of repairing these issues, which involved removing the White Wire entirely and using a new 10 guage Wire for the Blue Power feed to the CDI. She started right up so I took her for an 18 mile ride with no more electrical problems...
  19. happycheapskate

    happycheapskate Active Member

    This is interesting. Is there a lot of ignition parts problems with the Flying Horse brand? They basically look the same as Grubees to me. What is the difference?
  20. dinoseer

    dinoseer New Member

    I don't think it is necessarily the brand, but how fine and tiny the wire is coming from the Magneto Coil and soldered to the Top Arm. Vibration from these 2-stroke Motors is pretty significant and I would think break any tiny copper wire such as this. I was just able to figure it out, luckily from reading many posts in this forum.