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J 4 magneto question

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Author  [Modern View]

02-18-2017 04:56:58

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I never fooled with a mag. A project cub I recently acquired it has a mag and no starter. So my idea is to leave it hand start with the mag and not use a battery. How do I test the magneto without it on the engine? The engine is currently in pieces on my workshop floor lol.

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john *.?-!.* cub owner

02-18-2017 11:00:27

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 Re: J 4 magneto question in reply to jsfarmall, 02-18-2017 04:56:58  
Editing does not work, and I forgot to mention the impulse should trip 2 times per round of the impulse shaft.

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john *.?-!.* cub owner

02-18-2017 10:59:09

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 Re: J 4 magneto question in reply to jsfarmall, 02-18-2017 04:56:58  
You have learned one way to find if it hurts, but to find if it will fire a spark plug, clamp it in a vice, and connect a wire and spark plug to the coil cap.and ground the plug to the magneto body. put a ratchet and socket on the nut that holds the impulse and turn it till it trips. If you get a good hot spark you know the points, condenser, coil, and impulse are all good. Note, if it has been setting an extended period the points may need filed or replaced, and coil may also be weak. Coils are expensive.
Once you have good spark from the coil cap, connect wire back to distributor cap and use plug wires and spark plugs to see if it fires the plugs in order 1-3-4-2. There is not a spark safety gap built into the J4 or H4 mags, so it is not recommended to trip them without someplace for the spark to go.

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KL in Wi

02-18-2017 05:17:46

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 Re: J 4 magneto question in reply to jsfarmall, 02-18-2017 04:56:58  
Well, you could do like I did years ago. I clamped the mag in a vice, put a spark plug wire in it and told a (friend) of mine to hold the end of the wire and put one hand on the vice. The mag only had to snap once for me to know it worked. Poor guy hasn't trusted me since.

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02-19-2017 07:54:29

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 Re: J 4 magneto question in reply to KL in Wi, 02-18-2017 05:17:46  
That's hilarious! That's for sure on way to do it.

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tom dowling

02-18-2017 09:07:01

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 Re: J 4 magneto question in reply to KL in Wi, 02-18-2017 05:17:46  
thanks for the laugh... my older brother used to test them that way on me when I was a kid.

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