Killing Magnetos...

Discussion in 'Electrical' started by Qui Gon-Jinn, Sep 30, 2013.

  1. Qui Gon-Jinn

    Qui Gon-Jinn New Member

    3rd magneto in 4 weeks. Original died due to water. 2nd one was Sat night, heard a pop and lost power. 3rd one tonight.. pop, loss of power.

    Any indication of what causes this?

    I have another ready to be installed just need the time. But I don't want to put a new one on every single day to get myself to work and home. Seems that something else is wrong.


  2. jaguar

    jaguar Well-Known Member

    Could be a problem with the CDI pulling too much current from the coil causing it to overheat. Or you could be using the stator coil to power lights causing it to overheat.
  3. Qui Gon-Jinn

    Qui Gon-Jinn New Member

    no lights.. All my lights are stand alone battery powered..

    CDI Box might be a clue.. I have a spare one ready to go.. Change that and the magneto tomorrow..

    And.. order replacement spares..
  4. jaguar

    jaguar Well-Known Member

    Instead of throwing good money after bad why don't you buy my CDI?

    funny story as backup:
    In high school lunch line I saw the beans had a worm or two so I took the plate back to the lady dishing them out in order to complain. Being the brain-dead person she was she asked me if I wanted some more beans and I replied with astonishment that no, I don't want more wormy beans!!!
  5. Qui Gon-Jinn

    Qui Gon-Jinn New Member

    I will look into it further.. however as it is going to take 2+ weeks to ship it and the cost is five times what a stock is (that I have in my hands right now) I will go with my spare CDI. I have a local source that I get really great pricing from (comparable to online) and I try to support him.

    I just made some deals to generate some cash. Looking at resolving my other issues and getting a vehicle. If I do that the bike will be used about 1/2 of what it is now. I enjoy the rides but my schedule could use a 10 min drive to work over a 30 min drive on certain days. Working overnights means sleeping is a rare commodity at times.

    Thank you for the suggestion.
  6. Fabian

    Fabian Well-Known Member

    It's interesting how some people have no end of failures and other people don't. My experiences have had only a single magneto fail in 50,000 (30,000 miles) of riding. I have never had an original CDI fail and i have only had one Jaguar CDI fail.
    Having said that (and prior to the newer style big end connecting rod with crowded needle roller bearings) i suffered a never ending set of big end connecting rod bearing failures, which were caused by the incorrect ignition curve of the standard CDI. The Jaguar CDI fixed the problem but other people have never experienced a big end connecting rod failure, even with the standard CDI.
    Last edited: Oct 1, 2013
  7. crassius

    crassius Well-Known Member

    have you tried prying up on the end of the crank that the rotor is attached to - it may be a bad bearing causing this
  8. jaguar

    jaguar Well-Known Member

    Fabian you probably were just stressing it out more than other people by hauling that trailer around and climbing all those hills. Maybe you are weighty also, I don't know. But either way if the standard timing was right you wouldn't of had those problems. You fixed it by putting a "correct" CDI on it.
  9. BigBlue

    BigBlue Active Member

    I assume magneto, you are referring to the magneto coil and not the magneto rotor - there is a difference and helps when talking the same language. I am also assuming you have a Skyhawk style engine with the external CDI and not the StarFire engine with the internal CDI. I believe the StarFire had magneto coil problems.

    It's possible that your engine doesn't have a good ground or your magneto coils aren't grounded to the engine case. Another possibility is the lack of continuity with the spark plug and spark wire. If the CDI discharges and there is no continuity, you may end up frying your magneto coil.

    Good Luck,

    AKA: BigBlue
  10. Fabian

    Fabian Well-Known Member

    This is my strong belief regarding the majority of magneto and/or CDI failures.
    I have seen this situation more than once where someone is working on their engine (not necessarily a bicycle engine) and they either forget to attach the spark plug lead to the spark plug or they spin the engine over without the spark plug installed (to test or to check mechanical action) which in turn causes a high voltage pulse to back-feed through the system, thence finding a path to ground; in the wrong direction.

    Either the CDI and/or magneto fails "on the spot" or it fails a short time later, of which the ignition system is labelled poor quality by the operator.

    A faulty electrical connection between CDI and/or coil and spark plug will also cause a similar condition. The first point to check is the connection between spark plug lead and the screw-in-terminal on the CDI or ignition coil.
    Sometimes it appears to be firmly affixed but if giving the lead a slight tug, it will pull straight out, which requires the end of the spark plug lead to be cleanly cut back by approx 10mm (3/8 inch) and reaffixed onto the screw-in-terminal, which (sometimes) can be a lot harder than it sounds.
    Last edited: Oct 1, 2013
  11. crassius

    crassius Well-Known Member

    note also that the new 2-wire coils seem to have no soldered ground for the coil - not sure yet if both windings are there but not used or if it is now just one winding - either way, the screw making the ground is much more important now