Magneto coil failure?

Discussion in '2-Stroke Engines' started by bjs, Dec 18, 2008.

  1. bjs

    bjs New Member

    I had been riding for 15 minutes or so today, the engine was not that hot as I'd only been crusing at about 30km/h along a bike path. I was slowing down to cross a bridge, I hit the clutch and the engine stalled - and will not start. I think it is an ignition problem.

    The magneto coil (this is a Zbox/happytime engine), only measures 244 ohm instead of about 340 ohm as it used to. It also looks much blacker than when I last looked. So I'm guessing this is the problem.

    I don't understand why it failed. I don't have the normal kill switch hooked up, so that can't be the problem (I have a switch wired in series with the blue wire instead).

    Perhaps it was previously damaged by overheating on a longer trip and this was simply the straw that broke the camels back?

  2. Skyliner70cc

    Skyliner70cc Active Member

    Its possible that it overheated and the varnish laqueur that is used as the insulation on the coiled wire "burned" causing a short in the wire.

    I carry a spare magneto and CDI with me on long trips in my "tool bag" just in case. I've only had one CDI fail on me, never had a magneto fail (that I can recall), but can definitely say that I have had 1/2 dozen or so chinese spark plugs fail internally.
  3. bjs

    bjs New Member

    I think you might be right.

    The NGK spark plug is fine if not covered in a bit of carbon due to not firing. I tried one of the chinese plugs (that I never actually used), with no difference.

    I'm ordering a spare CDI box anyway.
  4. machiasmort

    machiasmort Active Member

    Want to know if it's your mag??? Connect a V meter to both leads comming from the block(your mag). Pedal like the ****ens and dump the clutch. Check your V reading. If you get 5V or above it's something after the mag. Use alligator clips on your test meter and be careful not to get tossed over the handle bars!
  5. machiasmort

    machiasmort Active Member

    definitely say that I have had 1/2 dozen or so chinese spark plugs fail internally.

    Most failures are caused by cracks in the ceramic. If you ever want to mess w/ a friend, use a real lead pencil and draw a line from top(metal) to bottom (metal) on a spark plug and the motor won't start,(same as a ceramic crack), It's a direct short, not providing a spark!
  6. flharleycop

    flharleycop New Member

    checking the magnito

    you said to use the volt meter when peddeling the bike, can you take the spark plug out so there is no compression and still get an accurate volt reading off the mag? Seems it wouldnt know the plug is out, But I think I may have the same problem. I have no spark after a ride it stalled after about 10 running. I had just finished washing it and was returning from a ride. Today when I took the side cover off some water came out so I could of got wet. I need to figure this out. I have no spark or very intermittent.

  7. duivendyk

    duivendyk Guest

    It's dangerous to crank engine without a plug connected to the ignition output,or with an air gap to ground of more than 1/8" The voltage will go sky high and zap the pulse transformer.Goodbye CDI. These transformers are marginal &prone to fail.
  8. BoltsMissing

    BoltsMissing Active Member

    Moisture can get in past the magneto cover and short everything out.
    So if you went through a rare puddle of water etc. I had this happen and unfortunately letting it dry out over night did not work either.

    I know on some CDI systems, manufacturers insist on using the "R" as in Resistor Spark Plug.
    Not sure of the terminology, but something to do with the spark traveling backwards up through the plug and back into the CDI, then fizzles out everything electronic in it's path.
    I think the sparky experts may be able to clarify this.
    A "Resistor Spark Plug" is usually the same plug number, except it would have the letter "R" added.
    I have not used "R/Plugs" on HT, only on other engines as strictly specified.
  9. duivendyk

    duivendyk Guest

    Resistor plugs reduce RFI,the electromagnetic energy created by the spark electric discharge is dissipated in the resistor.The same thing can be acomplished with resistor wire in the plug cable,if the plug cable is leaky some portion of the firing pulse may be bled off because of the higher source resistance,--the resistor wire-- and keep the plug from firing.Cheap resistor wire plug cables are prone to have this problem (poor isolation).If the plug itself is leaky,resistance plugs could have the same effect.Moral, use good quality cable & plugs,and seal CDI against moisture infiltration(hermetic seal,silicon rubber). Then resistance plugs are no problem and reduce RF pollution a lot.If a CDI unit has had moisture penetration,you can try to dry it out,bake in low heat oven for a couple of hours,usually does not work,once moisture gets in it's hard to get it out for some reason or other.Most likely, pulse transformer allready shot.
    Last edited by a moderator: Mar 11, 2009
  10. BoltsMissing

    BoltsMissing Active Member

    duivendyk, what you is say it right, but I'm reading off a user manual of a particular brand of MB
    It's in bold,
    Exact wording says,
    This particular MB, I was asked to check it out by it's previous owner
    ( not a HT). When I checked for spark there was none, so I rang the manufacturer and was asked what plug is currently being used. I told them it is not the Bosch as specified. When they sent the new CDI unit, it ran and still running today. Had the old CDI checked by a sparky out of curiosity and sure enough, it was fizzled, both CDI and the Coil/Magneto as well.

    That's why I am saying, there might be a hidden issue, where sometimes that flare up as you describe may backlash back at the HT CDI ?
    Last edited: Mar 10, 2009
  11. duivendyk

    duivendyk Guest

    I think the HT CDI unit is pretty marginal,that is underdesigned.It's sort of 'pot luck' with these things,depending on the components used.Some may last a long time,moisture in high voltage circuits is murder because of high dielectric constant of water (80!).May be the prudent thing is to bake them at low heat first and then encapsulate them in silicon rubber.The ignition cable entry is particularly vulnerable because it goes to the pulse trafo.
  12. michaelb

    michaelb New Member

    Please need help. Is my magneto bad? I got this bike from a guy who said he never got it to run. I've gone through pretty much everything; tank, carb, gaskets, plugs, and the most I get is a few farts. I checked the spark and it does get spark but it doesn't seem too strong. if I hold the plug, the electric shock is not bad at all, nothing like my lawnmower that gives a good snappy jolt. I also have a six volt headlight wired up and on a push start it does light up. I have a switch on the light so it is not always on. What are the chances the magneto or the magnet are bad? mikes
  13. Al.Fisherman

    Al.Fisherman Active Member

    Magnet bad?? never seen one go bad in my lifetime. Take a screwdriver and watch the magnet snatch it when you get close. Disconnect the light totally and try to start again. Actually sounds like a weak magneto but you can check that by spinning the engine over (pull) or take plug out for easier revolution. Check voltage output. Between 6 and 7 volts. If good voltage I'd check the magnet key and after that the CDI.
  14. Al.Fisherman

    Al.Fisherman Active Member

    If checking magneto this way, remove the plug for easier peddling. Tape plug to frame with the CDI wire and boot hooked up.
    Last edited: Apr 20, 2010
  15. michaelb

    michaelb New Member

    After trying just about everything and rebuilding or replacing just about every component it was suggested to look at the magnet/timing. There was no key in the magnet/crankshaft. Timing was nowhere. I bought this bike as a non-runner and the seller said he never had it running. Maybe it came from the box that way. Anyhow now it runs; now if I can only keep the chain from jumping off. mikes
  16. tacoshell4

    tacoshell4 Member

    haha so u added a key and it ran?
  17. 210061741

    210061741 Guest

    1 time i bought a GT-5 and the key was really small.

    the magnet was floppin around.

    I put a new key in it.
  18. Al.Fisherman

    Al.Fisherman Active Member

    Glad you checked your key. After re reading my post I see that I meant to say "if NO voltage check the key" and NOT if "good voltage". I've worked on just about any engine imaginable from these HT's to large 2 cycle outboards, small 4 cycle to big block V-8's and throw in a few diesels and these HT's have to be the easiest to diagnose and repair.
  19. danlandberg

    danlandberg Member

    Two CDI coils in one day

    :confused: I have about 70 mi on an engine before the rear mount stud broke off. I put my 2nd engine (new in box) and rode it for about a week, stopped at the store and it started and went about 20 feet and died & would not start again would pop about 5 revolutions and then nothing (like it was not getting enough fuel. Peddled it home and checked carb and nothing was clogged, fuel flow was OK. Took the CDI from the still in the box kit, Then it ran for 15mi. The same thing happened. I then checked the resistance of the mag. The manual said it should read 323ohms blue to black & 2.3ohms black to white. Mine read 346ohms blue to black & 5.9 black to white. The readings on the engine I took off were 338ohms blue to black & 2.5ohms black to white. That's closer to the book. I now need a CDI! :icon_cry: The engine(s) ran good until this! I am starting to really dislike the F-ing Horse junk. :veryangry: And the manual counterdics itself on how to hook the kill switch up. Pg 05 step 6, hook 1 kill wire to 1 CDI wire & the other wire to the other CDI wire. Pg 7 step 9, hook 1 kill wire red/yellow to white & green kill wire to ground. How do you check the CDI? ANYONE know? :confused:
  20. Al.Fisherman

    Al.Fisherman Active Member

    Dan, can't help on the CDI but both ways of hooking up the kill switch will work, I use the wires on the CDI on all my builds. I've had I CDI go bad and that was within 3 days of receiving the kit....Hence my signature on "Luckyearlybird"

    Got this off of another forum......

    All of my honda OEM service guides, Xrs, XLs, Nxs...

    all have the same wording..

    If the CDI is suspected to be bad, the only reliable way to test it is to swap it for a known good unit. If the bike runs, the former CDI is bad. NO S**t

    OK Dan... Tell me why the engine stud broke... How did you have the engine aligned with the frame...
    Last edited: May 5, 2010