Magneto coil;

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t6R

New Member
Mar 31, 2014
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Connecticut
Is the magneto that comes on the kit that doesn't have Red/blue and white wires ground in 2 places? Before i play with it i want to know. My engine won't start. I grabbed a volt meter and i've got nothing coming out of the leads on the magneto so its either the ground wire isn't properly done, or the magnet is too weak.
 

Slogger

Member
Sep 8, 2014
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nohio
If your magnet isn't spinning you won't see any voltage from the magneto.
There are three wires, typically the blue is the output for the CDI, black is ground, and white is a tap off the coil to provide juice to lighting which most don't use.
Picture a coil of wire wrapped around an iron bar hundreds of times. That's all the coil is.
When a magnetic field moves through the coil, a voltage is induced in the coil. When it's still, nothing is generated.
A multimeter will show all three going to ground when the engine is stopped. The difference is the black is grounded with 0.00 ohms to ground, the other two will show less than an ohm of resistance to ground. Mine reads about .485 ohm on the blue wire. The coil is just a piece of wire when it isn't in action, so this is what you see.
Hope this helps.
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
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Phoenix,AZ
Is the magneto that comes on the kit that doesn't have Red/blue and white wires ground in 2 places? Before i play with it i want to know. My engine won't start. I grabbed a volt meter and i've got nothing coming out of the leads on the magneto so its either the ground wire isn't properly done, or the magnet is too weak.
This is the 3rd time I'm posting this simple troubleshoot in this forum is 3 different topics.

Forum Search is your friend.

My troubleshooting procedure is simple these days.

Disconnect everything (CDI, kill button and spark plug).

Ohm the black magneto wire to a head bolt, it should read a dead short.
If not, check the ground tab on the magneto.
Note:
The new skyhawk CDI's have no white wire, ground is the lower connector but it has a wire from it to ground.

Old style mags with a white wire have a tab out of the mag that solders directly to the mag base and they can come loose, just hold it down and re-solder.

Ohm the magneto from the black and blue wire, 320-380 ohms is ideal, an open or dead short means a bad magneto if the wires are connected.

Ohm the CDI in the 10K-20K scale.
Red+ meter probe to CDI black wire.
Black- meter probe to the spark plug cap.
You should get about 6.9K ohms.

If not it could be a bad wire or cap.
Unscrew the plug wire at the cdi, use pliers or even cut it off and dig the junk out if need be and do the same test above again to the cable screw on the CDI.
If that works get a new wire and plug cap, if not you have a bad CDI.

If all of that is good there is only one thing left, the magnet.

That was indeed the problem with this repair on a new build with a 2014 gasbike.net front page engine kit.

When you pull the 4 bolts out of the magneto mount it should slam itself against the magnet, I mean to the point where it is hard to even get your first bolt in.
A weak magnet that lets you move the mag around pretty easily is not strong enough to create a spark which is what this repair had.

Magnet replaced, problem solved and my repair is done.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
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USA
old mags had brown/blue/black with brown being the output to the CDI - later mags have blue/black/white with blue going to CDI and sometimes missing the white

only mags I've seen with a red wire are 'super rat' internal CDI models - I have one here that I can try testing if that is the info you need
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
had a chance today to check the internal CDI

POS has the ground on the red wire??!!?? and the black is the output coil (which should measure about 600ohms)

I think that if I have to deal with many of these, I may change the wiring to put ground on black & hot on red.
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
had a chance today to check the internal CDI

POS has the ground on the red wire??!!?? and the black is the output coil (which should measure about 600ohms)

I think that if I have to deal with many of these, I may change the wiring to put ground on black & hot on red.
That's interesting, crassius. Back some time ago there was a guy who had a Super Rat that he couldn't get running. Someone suggested switching the wires and he came back and reported that it worked. Maybe now we know why.
Thanks for the heads up. Not many but there are a few SRs out there. Your advice might help them.

Tom
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
not sure it is sr or just same as - engine is new build with balanced crank & H2 top end made by a friend of mine who is also a retired mechanic

we may see more of these
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
57
48
Phoenix,AZ
Odd duck engine you have there but one thing is common.
The connection on the mag that is a dead short to the head is ground.