IH 1975 Cub, no spark past coil?

Anonymous-0 · Jul 18, 2013

Working on a 1975 12 volt IH Cub and have spark up to positive side of coil only. Do not have spark on negative side of coil with the ignition on or when trying to start the engine. Therefore, no fire to my new points, spark plugs, etc.

Have changed the coil two times (one used and one new) but still no spark. Can not figure out what the problem is.

What is my next step, don't know what else to do?

Any assistance will be appreciated. David

Bob · Jul 18, 2013

Ignition "ON", points "open", you should have battery voltage at BOTH low tension terminals on the coil.

Ignition "ON", points closed, you should have voltage at the "ignition switch" side of the coil and NO voltage on the distributor/breaker point side 'cuz that end of the winding in the coil is connected to chassis ground through the breaker points.

Whip out a test light and see what's going on on the points side of the coil with the points open, then with them closed, and post back.

If NO voltage on points side of coil with points "open", insulator at distributor terminal may be shorted, condenser may be shorted, or something else in that area that is NOT supposed to be touching ground may be out of place, and grounding.

To gain a good understanding of how Kettering ignition systems work, take a look at the John Deere FOS-20 manual for ignition systems.

(It's OK to look, it's posted at a Cub site!)

http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/FOS-20%20Chapter%206-Ignition%20Circuits/index.html
Sparky FOS

John T · Jul 19, 2013

With the ignition on and voltage present on the coils high input (NOT to dsitributor) terminal, theres (if all is well) usually no voltage on the coils output to distributor BECAUSE THE POINTS ARE USUALLY CLOSED and thats grounded out....

If you put a test lamp on the coils output to frame and with ign on if you slowly turn the engine over the light should flash ON (when points open) and OFF (when points are closed) otherwise shes not gonna fire!!!!!!

So I dont have to re invent the wheel each time this question gets asked, which it is almost daily sometimes, SEE MY TROUBLESHOOTING PROCEDURE LINKED BELOW

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition Troubleshooting

mkirsch · Jul 19, 2013

You should only get actual "spark" out of the center post on an ignition coil. The two terminals should have "juice," or more appropriately "power," which means that a test light will light if you connect it, or you will read voltage on a voltmeter.

If that's what you meant I apologize.

Have you pulled the center wire off the distributor cap and held it 1/4" from the engine block while cranking? No spark there?

Points could be glazed over, or set too close.

Did you change the condensor?

El Toro · Jul 19, 2013

Rub the points with some 320 wet or dry then see if the engine will start. Hal

Rumplestiltskin · Jul 19, 2013

David:

I had the exact same symptom yesterday with a Ford 881. The problem turned out to be a small amount of dirt/rust/tarnish on the center "button" in the distributor cap, where the button contacts the rotor.

Mark W. in MI

IH 1975 Cub, no spark past coil?

Anonymous-0

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Bob

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John T

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mkirsch

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El Toro

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Rumplestiltskin

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