Magneto coil burnout

biknut

biknut

Well-Known Member
My new Flying Horse motor seems to be having a problem with magneto coils. So far I've burned up 2 of them in a little over 500 miles.

None of my other china girls have ever had any electrical trouble.

Both coils developed open windings. In both cases the failure occurred during high speed operation.

The first one failed intermittently. The motor died, but after a little cool down, restarted. Had a repeat failure the next day, and again restarted after cooling, but took little longer this time. The next day if failed again, and this time it was permanent. The winding checked open. I replaced the mag coil, and the CDI.

So after replacing the mag coil, and CDI, it ran fine for a few days. Then yesterday I was running hard again and all of a sudden, flame out. After pedaling home, the new magneto coil checked open.

I'm trying to figure out why this is happening all of a sudden with this motor.

So far this is our working theory. The magneto coil may be burning up from too much current, caused by a combination of high revs, and a rotor magnet that's too strong. The rotor is the only part I haven't changed.

One suggestion is to close the spark plug gap a little, which may cut down on the current requirement.

Any other ideas are welcome.
 
i gap my plugs between .25 and .28 so less power is needed to jump the gap never had a problem burning up cdis or mags
 
Look at the Great Magneto Mystery from Grubee. There seems to be two type of magneto coils being produced. The newer one is more powerful than the older one. The newer magneto coil needs to be sanded on the backside to remove the varnish and the magneto coil needs to be grounded to the frame. Your problem may be caused by the magneto coil not being grounded. Just a theory. I don't know if your magneto coil is the old or new one.

http://www.grubeeinc.com/USA/Magneto Mystery.html

Good Luck,

Chris
AKA: BigBlue
 
BigBlue said:
Look at the Great Magneto Mystery from Grubee. There seems to be two type of magneto coils being produced. The newer one is more powerful than the older one. The newer magneto coil needs to be sanded on the backside to remove the varnish and the magneto coil needs to be grounded to the frame. Your problem may be caused by the magneto coil not being grounded. Just a theory. I don't know if your magneto coil is the old or new one.

http://www.grubeeinc.com/USA/Magneto Mystery.html

Good Luck,

Chris
AKA: BigBlue
Click to expand...

Thanks for the link. All of my mag coils are the new type. The first one that failed was new. The second one was used, but known to be good.

The third one is slightly used and known good. It's working fine at this time.
 
so ive run into the same problem as you cept its happened to 2 bikes. there the same motors on both only diffrence with em is the first bike had an ngk plug in it mag and cdi fried second bike had an auto lite plug but i swapped that plug to the first bike and put the ngk in the second bike now that one wont run and just died on me i still have to test the mag and cdi.

but this is the second ngk plug that ive had problems with first just died on me after a month and now this one seems to be frying my mags and cdi havent had a problem with auto light thou.
 
I've lost a total of 3 mag coils in the last month. All of them went open. I disconnected the kill switch when I installed the last one, on Monday.

I can't understand why this is all of a sudden a problem, but my theory is the magnet rotor might be unusually strong on this motor, making the mag coil run hotter than usual. Them when I hit the kill button it pushes the coil winding over the edge.
 
ah that is possible but ive been running with the kill switch disconnected cause my handle bars are to long at the moment to reach the connection. for he moment im gonna stay away from ngk plugs till i can get a few more parts since it seems that those plugs my be causing a me a problem. since my motor was running great with the auto lite plug but when i put a bp6hs ngk plug in it started running funny.
 
hi, i'm in west michigan (the other west coast) and have a CDI problem. my new skyhawk has about 2mi on it. my mag checks OK per mag mystery. instaled 2nd CDI still no spark. is this a quality control problem? od we have a bunch of CDI that ain't worth a *&^(*&^*&%*^&%E%$#$$#@(*&??!
 
try a different spark plug also when your checking mag readings make sure you check using the motor as a ground sometimes there's not a good enough ground to the motor to get a good spark.
 
tryed 3 prong plug stock and champ. checked gnd from black to allover block and mag.all good. good ohm reading from blue to black. ohm readings on CDI swow it is defective. is there another cdi unit that will work on me 66cc ? i think i need to order a new one. thanks. i'm really flustrated-bike #1 ran really good,#2 not so much.
 
8-9-duck said:
hi, i'm in west michigan (the other west coast) and have a CDI problem. my new skyhawk has about 2mi on it. my mag checks OK per mag mystery. instaled 2nd CDI still no spark. is this a quality control problem? od we have a bunch of CDI that ain't worth a *&^(*&^*&%*^&%E%$#$$#@(*&??!
Click to expand...

How much resistance are you reading through your mag coil? Black to blue wire.
 
bik i agree with you that the mags are getting way to hot just went for a 20 mile ride and towards the end my bike started acting up. ended up having to pedal the last mile and a half home good thing its down hill. originally my mag had a bad solder joint, i repaired that and no more problems i think the mags may get a little hotter with the ngk plugs because they have a higher resistance than the auto lights or champ plugs. so with this next mag im gonna try running a champ plug and see how it goes.
 
desolation said:
bik i agree with you that the mags are getting way to hot just went for a 20 mile ride and towards the end my bike started acting up. ended up having to pedal the last mile and a half home good thing its down hill. originally my mag had a bad solder joint, i repaired that and no more problems i think the mags may get a little hotter with the ngk plugs because they have a higher resistance than the auto lights or champ plugs. so with this next mag im gonna try running a champ plug and see how it goes.
Click to expand...

I'll have to consult with an expert about that. I'm not aware that NGK plugs have more resistance than other plugs.

I've been using the same NGK plugs for 2 years without any problems. Same kill switch too. The only part that's different is the rotor.

An electrical expert friend of mine looked over my system, and said the way the kill switch is wired may be the problem, because when you hit it, it shorts the mag coil wires together. The problem with that is, until the motor actually stops turning, it still puts voltage on the coil winding. If the winding is already hot, it might be able to push the windings over the edge.

That being said, it's never been a problem in 2 years, until now. The only difference I can think of is the rotor.
 
i just went and bought a few new plugs and checked the ohms on all of em the one ngk plug i had was reading 13ohms while my others ranged from 1 ohm to 5 ohms i changed out the ngk plug that was reading 13 ohms and haven't had a problem with my mags and cdi yet getting close to a month now about a week out from being a month using the new plugs with no problems
 
I'm thinking the problem is caused by the kill switch. After the third coil burned out I disconnected the kill switch, and I haven't had a problem since. I'm still running the same NGK plug as always.
 
i don't run with the kill switch haven't for 2 months, i think mine was just a bad spark plug.
im still running a ngk plug but its a bpr7hs instead of a bpr6hs. the bpr7hs reads 5kohms and the bpr6hs reads anywhere from 10kohms to 15kohms. so im pretty sure something was wrong with it as soon as i changed spark plugs it ran smoother.
 
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