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Small Air Cooled Gasoline Engines

Johnson Utilimotor Dead Coil


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  #1  
Old 05-04-2018, 06:39:45 PM
overdriver overdriver is offline
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Default Johnson Utilimotor Dead Coil

I have a friends utilimotor

he asked me to look at
it doesn't have any spark
I aggressively cleaned the points
and checked connections
it is the dual coil fg I believe
are they known to have bad /weak coils ?
how should I test them
any words of wisdom
thanks
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  #2  
Old 05-04-2018, 07:05:59 PM
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Default Re: johnson utilimotor dead coil

That style magneto is basically a rotary version of the wico EK. If the center drive armature has been removed the outside magnets will loose magnetism. You can recharge them by installing the armature and charging. Then DO NOT remove it again!! The coils can go bad and I think wico ek coils will fit.
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Old 05-24-2018, 06:11:38 PM
overdriver overdriver is offline
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Default Re: Johnson Utilimotor Dead Coil

I have found both coils seem to be dead (no resistance ) with ohm meter
can any one explain how this mag works with 2 coils in series ?
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Old 05-25-2018, 02:04:43 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Johnson Utilimotor Dead Coil

Basicly, the same as a single coil. One side of the primary is grounded and goes to the second coil. the other side of the second coil goes to the points. when the points open, the magnetic field collapses and generates current and voltage in the secondaries. they are grounded on one side, then linked together, and the other side goes to the plug. As magneto building was in its infancy, the manufacturers didn't have the tech to build a single strong coil, so they built 2 weaker ones in series to make due. you should tyr and replace the condenser as well. When you OHMed the coils, did you check each coil separately, or twinned? As there are less turns due to construction, you may get lower values that a 'regular' coil. Also, be sure the wiring linking the 2 coils is intact. An open will show no resistance.
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Old 05-25-2018, 04:23:00 PM
JoeCB JoeCB is offline
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Default Re: Johnson Utilimotor Dead Coil

To clarify for my own understanding what AM described. Two coils, end to end on the same armature. I presume that one is the primary (low voltage and to the breaker points) winding, the other coil the secondary ( high voltage) winding. If so, then resistance thru the primary should be very low ( 1 - 2 ohms) , resistance thru the secondary high ( 2 K - 5K ohms). Is this correct?


Joe B

Last edited by JoeCB; 05-25-2018 at 09:54:52 PM.
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Old 05-25-2018, 06:22:41 PM
overdriver overdriver is offline
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Default Re: Johnson Utilimotor Dead Coil

hi folks
I checked both separately
comparing results to a good mag with good coils
now to find a new replacement set

I read somewhere a long time ago you could
make the mag work on one coil
but I am not sure how one could do that
I would think the timing may be off
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Old 05-25-2018, 07:00:47 PM
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Junkologist Junkologist is offline
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Default Re: Johnson Utilimotor Dead Coil

Quote:
Originally Posted by overdriver View Post

I read somewhere a long time ago you could
make the mag work on one coil
but I am not sure how one could do that
I would think the timing may be off
The coil or coils have nothing to do with the timing. It’s the moment when the points open that determines the timing of the spark.
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Old 05-26-2018, 11:05:05 AM
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Default Re: Johnson Utilimotor Dead Coil

Here is a link to a website that sells a single coil replacement.


http://www.magnetoparts.com/wico_fw.htm
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Old 03-08-2019, 05:48:24 PM
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Default Re: johnson utilimotor dead coil

Quote:
Originally Posted by turbo View Post
That style magneto is basically a rotary version of the wico EK. If the center drive armature has been removed the outside magnets will loose magnetism. You can recharge them by installing the armature and charging. Then DO NOT remove it again!!
Sorry, noob here, not understanding how to recharge the magnets? Thansk for your help, old dad
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