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troubleshooting a wc magneto

B

BUSHNELLMAN

Member
I have a FM jb4 magneto I'm trying to figure out, cant get a spark out of it, I have read all I can find on the topic and need to know how to troubleshoot it.
for one I cannot see a "beveled" tooth on the drive gear to line up the top gear, I think I see a dot on one tooth, is that it?
how much resistance should I measure when ohming out the coil?
or am I all wrong, looking at what I'm looking at, and where should I start to trouble shoot it ...Thanks!
 
The small steel gear should have the beveled tooth. The large gear
should have the letter "C" or maybe "CW" on one tooth meaning
clockwise. Don't line it up on the " CCW"

Coils are often bad in FB magnetos.
 
do you use a megger to check the resistance of the insulation, and if I ohm out the coil what kinda readings should I expect? I think I measured 4.5K ohms across the windings, and check the condenser like any other capacitor with my Fluke meter?
I just don't know if I'm measuring the right things!
 
Here's a photo of the gears. In The photo the beveled tooth is at 12:00 position. The bevel is just the very tip of the tooth
shown in red. My magneto the large gear the teeth are marked with a letter "A" and "C". You need to use the letter "C"

If your coil feels sticky to touch and is shinny looking like mine it is bad.
a162161.jpg

a162162.jpg

a162163.jpg

a162164.jpg
 
49512.jpg


Pinion may have the pip instead of bevel. See that the pip is indexed from the pin slot by the same number of teeth.
 
I have the PIP style, thanks Stu!
I think I understand the gear alignment/ setting and will make sure of that before I try again

I have measured the winding of the coil at 6/10ths of an ohm, do I need to meg out the insulation to see if the coil is bad or how do I test it? I have what I believe is the replacement coil on mine its the red coated one.

I measured the condenser at 240 micro F

Damn! I ohmed out between the brass rod on the cap to the center pin and it was open! I replaced the cap with new and made sure I had continuity, cant imagine what happened to that!

kill switch wire is not grounded

I will try for spark again tomorrow, one thing I think I was doing wrong was to expect a spark out my selected wire socket on each time I spun the gear when I need to turn it at least four times to get 1 spark, am I thinking correctly?

Hey thanks again ! wish me luck
 
(quoted from post at 06:06:07 06/06/17) You can send it to me as I have the coil & condenser testers and a magnet charger. I work cheap as a hobby.
Click to expand...

Thanks for the offer teddy but I want to learn this for myself, ya never know when it will come in handy!
 
I GOT SPARK!!!
turned mag over today and seen my first spark...I believe I have it timed correctly so Im gonna put it on the tractor!

next... should I stay with the 6V generator or switch to a 12V alternator?
any input would be greatly appreciated.

Thanks again!
Bushnellman
 
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