Checking coils on a Pony Motor

~There are numerous ways to test those coils but none are an absolute as the resistance can be within specs & they still won't work.

~If you have an ohmmeter try disconnecting both coil wire pigtails [on one coil] & measuring the resistance between them [you want over .75 ohm & under 3 ohms but not an open, & not a short to the secondary]..Caution: hold the wire terminals at the condensers while removing the pigtail wires as those condenser tops twist off easily�� Another thing to do is just measure & compare primaries [between the 2 pigtail wires] & secondaries [between the 2 plug wire towers] to see if both coils are close to each other. If the differ by much one coil is probably bad.

~The primary is usually the problem with those coils but the secondary could also have a problem [measure between the coil�s 2 spark plug wire towers using an ohmmeter & you need somewhere between 6K & 12K, again not an open or a short to the primary.

~A quick test is to remove the coil pigtails at both condensers, then verify you have battery voltage at the distributor�s power stud [6 volts with the wires disconnected from the condensers, 4+ volts with both coil [condenser] pigtails grounded. Then use a jumper wire & ground one spark plug wire on a coil & hook a known good spark plug to the other, then quickly scratch & remove the coil pigtail to a good clean ground, [if the coil is good the plug should spark].
~If the coils appear to be good in the above test you might just have a rusted up coil center core [both coils are mounted on the same center core] . You might want to pull the coils from the center core & remove all the rust from the core.

~Remember to get a spark from either coil BOTH plug wires & both spark plugs on THAT coil MUST be hooked up & laying on a good ground as those coils fire one spark plug positive ground & one negative ground so one plug on each coil acts as the coil�s primary side ground.

~If you have the early coils MAKE SURE both plug wires are firmly plugged into the back of the coils as they just push in on the early coils [on the later coils the plug wires screw in]. If one of those plug wires is pulled loose neither plug on that coil will spark.

~I usually ground one coil plug wire tower using a jumper wire while testing for a spark on the other as a failed spark plug wire can & will cause both plugs to not spark on that coil giving a false impression you have a bad coil.

~A word of caution: don�t leave the ignition switch on for long with both coils hooked up & the points closed while you are testing the system or you will definitely have bad coils [it doesn�t take long to fry one of those fragile coils].

~If you don�t have [or aren�t familiar with] a good ohmmeter just use your nose & the quick test in the above.. You can then use a 6 volt test light [or any 6 volt bulb] to verify the battery voltage on the distributor stud.

~If the coils test ok but the pony won�t start due to a weak spark you might have a broken [or disconnected] by-pass wire at the starter 70D or at the starter push button 720D. That by-pass wire increases the pony distributor voltage during cranking to compensate for lower system voltage during cranking. Those pony coils are sensitive to low voltage & drop their KV output pretty fast if they see low input voltage.

~I know this is a little complicated but isn�t that bad if you read through it a few times�It helps if you print this out & take it out to the tractor with you while working.

~Questions: [email protected]

Those coils have been known to go bad and become open, especially if the power is left on long periods with the engine not running (like forgetting to turn off ignition). Another common problem causign no fire (even if coil is good) is bad or burned or pitted or mis gapped points. Theres a voltage dropping ballast resistor in series in the ignition circuit which drops the 6 volts from the battery down to around 4.5 to 5 or so to feed the coils. If its open, theres never any voltage to the coils and they obviously cant work.

For them to work, there has to be power to the coil primarys input (via the ignition switch and a ballast resistor) and the coil primarys output goes to the points and gets a path to ground when the points are closed. Then when the points open to break the coils primary circuit, a high voltage is induced into the secondarys which fires the plugs.

If you place a test lamp on the coils primary high (not to points) side and turn on the switch, voltage should be present. If not, she cant ever fire the plugs and there may be an open in the circuit,,,,, , or a bad switch,,,,, ,,, or open ballast if theres never any voltage on the coils high (not to points) side. A test lamp or voltmeter at the points (lil terminal) should show voltage when the points are open on high cam, but go off when the points are closed if the points are good.

A test lamp at the points (same as coils low output side) should flash on and off as the engine is cranked over, and if it dont, the plugs cant fire.

If it never goes off, the points arent closing right (check gap and condition of points) or are bad or not getting a ground.

If it never comes on (ignition on and points open) the points,,,,, or the coil,,,,,or the condensor,,,,, or the circuit may be grounded out,,,,, ,,, or theres no power reaching the coil in the first place (bad switch or wiring or ballast open or open bad coil) and she wont ever fire either.

Turn on the ignition and test to see if there's voltage present to the coils high (not to points) side (A MUST) and if voltage on the coils low side at points goes on and off as the engine is cranked. Unless the coil is bad or open or shorted, if the voltage tests above pass, the plugs should fire when the points open.

There should be a low ohm DC resistance (around 1 to 2 ohms) on the coils low voltage primary circuit, which is between where the voltage is applied (via switch and ballast) and the lead to the points. If not or its an open circuit, the coil is bad.

Try those tests first to see if the coil is firing, but if not, the voltage and points tests may show why not and post back or e mail or call me (812) 824-4608 and I will help you more.

God Bless ya Neighbor

John T Nordhoff in Bloomington Indiana

Take a spark plug and Put it on spark plug wire. Put the end of spark plug on any metal on tractor and hold it perpendicular( BE SURE GET AWAY FROM FUEL)and then crank it up to see it it spark. If you check the points gap, condsenors, a wiring from the switch, spark plugs, spark plugs gap, and sparks plug wires. If all good, that mean coil is bad.

Be sure always turn the switch off when not using pony motor. If you don't, you gonna take your wallet out and buy another 2 coils
don't use 12 volt or the coils is cooking
Thanks
Tracy