Magneto coil failure?

[bjs]

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?

 

[Skyliner70cc]

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.

 

[bjs]

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.

 

[machiasmort]

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!

 

[machiasmort]

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!

 

[flharleycop]

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.

THanks

 

[duivendyk]

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.

 

[BoltsMissing]

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.

 

[duivendyk]

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.

 

[BoltsMissing]

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,

*NOTICE*
when replacing the spark plug make sure the genuine Bosch spark plug,
WR10FC is used. Failure to use the correct plug will result in damage to the electronic CDI unit.

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 ?