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Farmall & IHC Tractors Discussion Forum
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Identifying coil voltage

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jim

01-07-2004 05:23:05




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How do you tell if you have a 12v or 6v coil? I bought tractor converted to 12v, single wire generator, but no resistor to reduce voltage. So how do i tell if I need a resistor, or if I have a 12v coil?
Tractor starts great, idles great, but misses above idle, and fouls #2 and #3 plug. Outside of fuel problems, any ideas on what could be problem?




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Hugh MacKay

01-09-2004 03:04:43




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 Re: Identifying coil voltage in reply to jim, 01-07-2004 05:23:05  
Jim: When a Farmall gasser starts fouling 1 or more, but not all plugs, the number one thing on my mind would be compression test. I don't have a problem with the ignition advise you have received, good solid advise I would say. I guess I would have to side with Bob on the Champion plugs, it's all I ever use. Like Bob, I don't have a problem with the other brands either.



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Bob M

01-07-2004 11:54:10




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 Re: Identifying coil voltage in reply to jim, 01-07-2004 05:23:05  
Doug’s advice is right on. However if you don’t have an ohmmeter and your tractor has a numbered (not zoned) ammeter, you can determine what coil you have by simply watching the ammeter while you turn on the ignition. If the ammeter shows 3 – 4 amps discharge you have a 12 volt coil. However if it shows a discharge of 6 amps of or more you’ve got a 6 volt coil – plan to add a ballast resistor or swap it for a 12 volt coil!

To your misfiring and plug fouling issues, presuming your carburetor is properly adjusted it means the spark plugs that are too cold. Switching to plugs 1 or 2 heat ranges higher should eliminate the problem.

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Jim

01-07-2004 13:43:13




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 Re: Re: Identifying coil voltage in reply to Bob M, 01-07-2004 11:54:10  
Thanks, Bob.
Am using D21 plugs...hotter than that? Its a light duty tractor, not used under load at all.



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Bob M

01-07-2004 17:58:06




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 Re: Re: Re: Identifying coil voltage in reply to Jim, 01-07-2004 13:43:13  
Yeah - you might try the hotter D-23 plug. But D-23's can sometimes be hard to find. Or try another brand as others suggest.



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Doug in OR

01-07-2004 16:17:55




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 Re: Re: Re: Identifying coil voltage in reply to Jim, 01-07-2004 13:43:13  
You might try Autolite 388 plugs. My experience is that a Champions tends to foul more easily unless you work the tractor hard much of the time.



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Doug in OR

01-07-2004 07:39:29




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 Re: Identifying coil voltage in reply to jim, 01-07-2004 05:23:05  
One way to get an idea is to put an ohm meter across the two coil studs and measure. Disconnect the coil first, of course. You need a meter that is accurate, though. A 6 volt coil will show a resistance of about 1.5 ohms - a 12 volt coil will show a resistance of approximately 3.2 ohms. Ford and a few others had coils rated at about 8 volts for awhile, I believe. If your coil reads somewhere between the two above figures, it might be an 8 volt coil. In any event, you want approximately 3.2 ohms in your coil circuit - including any ballast resistor.

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