Coil talk.

641Dave · Jul 25, 2011

My tractor barely has the power to climb a hill.

I just replaced the distributer, points and condenser but no improvement.

I figure it's either a coil or plugged jet in the carb. which will be my next focus when I go back down to the property.

My question is, what does the resistor do for a 12 volt system which I have on my tractor.

Also, would any 12 volt coil work on my 641?

Kentb of SWMO · Jul 25, 2011

I do not know about Fords farm tractor BUT I do know that on their cars and trucks they always used internal resister coil. The resister in a 12 volt ignition system is to keep the points from burning up BUT you only use a external resister on a coil built to use a external resister. IF you are using a resister with a coil that is a internal resister type this could cause hard starting and low power. I would try taking the resister out of the system and see what happens. It you need the resister, because the coil IS NOT a internal resister type, the point will run very hot finally burning up.
If this tractor were mine, I would upgrade the ignition system to a Pertronix unit doing away with the point and condenser.

Kent

Bob · Jul 25, 2011

The resistor adds resistance to the primary circuit limiting current to a safe value for the coil and points. (Typically 3 to 4 Amps, ignition "ON", points CLOSED, engine stopped.)

"True" 12 Volt coils marked "no external resistor required" have enough INTERNAL resistance (typically about 3.5 Ohms) so NO external; resistor is needed. (Example NAPA part # IC14SB.)

12 Volt coils marked "Use WITH external resistor" are more or less the same as 6 Volt coils (with a primary resistance of 1.5 to 2 Ohms), and therefore need an external primary resistor of about 2 Ohms.

(NOTE... there is some variation in coil primary and ballast resistor values, these or round figures.)

BTW, I'll bet you find your "spark problem" in the fuel system.

Oh, yeah, also check that the distributor's speed advance is not stuck and is operating properly.

641Dave · Jul 25, 2011

Check and check!

Thanks guys!

old · Jul 25, 2011

Trouble shoot before throwing parts at it!!!!!!!!!. First off check your spark, it should be a blue/white in color and jump a 1/4 inch gap. Next pull the drain plug out of the bottom of the carb and make sure you have a good steady flow of gas for around 5 minutes. Catch that liquid gold for 2 reasons. #1 to look for dirt rust and water in it and #2 so you can use if for something other then grass killer. A couple other things to try what happens if you choke it??? If you choke it and it does not try to die on you your running to lean. Also if you do that you should start getting black smoke again if you do not to lean. Can you adjust the main jet needle to the point of getting black smoke?? If not then carb main circuit may be clogged up

El Toro · Jul 25, 2011

If you have a main jet adjustment screw you need to open that since this will enrich the fuel mixture. Even garden tractor and lawn mowers have that feature. As Old said that jet may be packed with dirt or rust or both if opening this doesn't help. Hal

36 Coupe · Jul 25, 2011

There is no such thing as a an internal resisted coil.There is no room in the coil for a resistor in side a coil.The extra heat would explode an oil filled coil.

641Dave · Jul 26, 2011

I think you have me well on my way.

I'm sorry this thread probably slides back to the whole "repeat" question thing and I'm sure I just ------ some of folks off with a simple coil question but every reply I just got here is going to help me save time by better understanding this simple little machine.

I really appreciate it fellas!

rustyfarmall · Jul 26, 2011

(quoted from post at 14:56:12 07/25/11) There is no such thing as a an internal resisted coil.There is no room in the coil for a resistor in side a coil.The extra heat would explode an oil filled coil.

If you are thinking of a ballast resistor that is normally mounted on the engine, you are correct in saying there is no room for it inside a coil, but resistors come in many, many, different sizes and configurations, and yes, there is such a thing as an internally resisted ignition coil that does NOT need an external resistor. I have one on my Farmall M that is converted to 12 volts, and that coil works very well, thank you.

Bob · Jul 26, 2011

Rusty, the point Coupe is trying to make is the same as I posted about... the TRUE 12 Volt coils are wound with more primary windings and do NOT use an actual resistor INSIDE the coil.

rustyfarmall · Jul 26, 2011

(quoted from post at 06:37:41 07/26/11) Rusty, the point Coupe is trying to make is the same as I posted about... the TRUE 12 Volt coils are wound with more primary windings and do NOT use an actual resistor INSIDE the coil.

My point exactly. It does not need an external resistor because the resistance (not resistor) is built in.

The manner in which Coupe is making his statement, although he is NOT wrong, will lead many folks to believe that an internally resisted ignition coil is just a myth, and does not actually exist.

36 Coupe · Jul 26, 2011

The internally resisted coil has been brought forth because a lot of dummies do not under stand the terms impedance or reactance.Your ignition coil operates in an AC circuit.The ignition points create an alternating current.

Coil talk.

641Dave

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Kentb of SWMO

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Bob

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641Dave

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old

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El Toro

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36 Coupe

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641Dave

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rustyfarmall

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Bob

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rustyfarmall

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36 Coupe

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