Re: troubleshooting a cub...help...

Posted by John T on November 23, 2005 at 13:46:29 from (66.244.90.98):

In Reply to: troubleshooting a cub...help... posted by Josh Hoffman on November 23, 2005 at 12:56:44:

Josh, if you were to remove the coil wire from the cap (leaving coil end attached in coil) and turn her n on crank her over, is there a good blue spark that will jump from the bare end of the exposed coil wire to frame ground if the wire is held about 1/8 away from tractor steel??? Thats to see whether or not the coil itslef is firing totally independant of any cap or rotor problems. If the coil wire always fires good but the plugs dont, its either a cap or rotor or plug or plug wire problem or else shes out of time such that the rotor tip isnt lined up with a cap tower each time the points break open to fire the coil.

If the coils not firing are the points gapped right and opening n closing as the engine cranks and the distributor shaft rotates???

When you say the points spark but it dies out after some seconds of cranking, do you mean they stop sparking?????????? If so I wonder how good the ignition switch is (may have a bad carboned resistive contact) so try to Hot Wire the coil (see below) to by pass any potential switch or Ballast Resistor type problems. If the points spark a while then stop and theres still and always good voltage present on the coils high input terminal (like you would definitely have if the coil were "Hot Wired") I wonder about the condensor even if you claim its new!!!!!! Remove the condensor wire off the points n crank her n see if they keep sparking each time as they should ??? If they do and the coil wire fires per the above test but that stops if the condensor is wired in place, REPLACE THE CONDENSOR.

I also wonder about the condition of the battery n starter n cables n grounds??? If the battery were weak or the starter were drawing excess current or the battery or starter or ground cables or connections were bad, its possible the batterys voltage is drug down so low after some cranking the coils not getting sufficient voltage???? Is she still cranking well when the points stop sparking or the coil firing????????? Is the battery like completely drained after cranking attempts???? If so, I would make sure the battery is good n well charged or try a known good substitute battery. To be safe you may wanna remove, clean n wire brush, n reattach each n every battery n starter n ground cable.

If the lights would dim down badly when cranking and the coil stops firing, YOU MAY JUST HAVE A BATTERY OR A STARTER OR A CABLE OR GROUND PROBLEM !!!!!!!!!!!!!!!!!! instead of an ignition problem. Then if the battery n starter n cables n grounds are all good but she stops firing after some cranking, I would suspect the ignition switch or a ballast (if it has one) which hot wiring would eliminate.

If the points are good and gapped proper and open n close as the engine and distributor shaft rotates, proceed as follows for troubleshooting.
NOTE some of this may be a repeat of the above, but I still wonder if theres good voltage on the coil constantly when the ignition is ON (GOTTA HAVE) or if not cuz theres a bad ignition switch or a bad Ballast Resistor (if it even has one??) However, if shes Hot Wired that would eliminate any switch or ballast type problems, so if it still dont fire even hot wired, proceed as below

1) THE VERY FIRST THING YOU GOTTA HAVE is constant voltage to be present on the coils high input supply (NOT to distributor) terminal when you turn the Ignition switch ON. If not she cant ever fire, but in the event the ignition switch or circuit/wire down to the coil or any Ballast Resistor is bad or open, you can HOT WIRE it by jumping a hot ungrounded battery voltage source to the coils high input supply (NOT to distributor) side n see if she runs then???? If she fires hot wired, you could have a bad ignition switch ((That can happen, when Ignition is on, the switches IGN terminal must turn hot n stay hot)),,,,,,,or an open Ballast (if it has one) or a bad/open wire from switch to coil.

If the switch is good, if you turn the ignition switch on and place a test lamp on the coils high (NOT to distributor) terminal SHE MUST LIGHT UP. If not again, look for an open Ballast Resistor (if it has one, it should read around 1.25 to 2 ohms across its terminals) or bad/open wires from the switches IGN output down to the Ballast (if it has one) and distributor.

2a) When the Ignition switch is turned on, voltage should appear on the coils high input side. That would be 6 volts on a straight 6 volt system or 12 volts on a 12 volt non external ballasted system, or around 6 volts on a 12 volt system that used a 6 volt coil plus an external Ballast Resistor and the coil is good and the points are closed and they and ALL wiring is good.

2b) To insure the coils low voltage primary winding is not bad/open, use an ohmmeter and measure its DC resistance between its lil + and -terminals. If its an open circuit (no continuity) its bad/open and will NOT work. It should measure around 1.25 to 2 ohms or so if its a 6 volt coil and maybe 2.5 to 3.5 if its a 12 volt internally ballasted coil. NOTE CAUTION have all leads and any voltage source DISCONNECTED FROM the coil for this simple primary winding continuity test.

3) Next, place your voltmeter or test lamp over on the coils other low to distributor terminal side, turn her on and crank the engine over.

4) A test lamp there should flash ON (when points are open) and OFF (when points are closed) as the engine is cranked slowly.

5a) If the lamp never comes on there, the coils primary is bad/open,,,,,,,,,,or the points are never opening,,,,,,,,,or theres a shorted/bad condensor (remove its lead to points and see if lamp comes on, if so, bad shorted condensor or its wiring),,,,,,,,or the points wire is shorted,,,,,,,,or the distributors side pass thru stud is grounded (use ohm meter to test that),,,,,,,,,or the points may have a shorted spring.

5b) If the lamp never goes off as engines cranked, the points are not closing or are bad,,,,,,,,or the wire or circuit is missing from the distributor to the points,,,,,or the distributors not well grounded to the tractor.

She cant fire the coil unless its low side is getting a conductive ground return path via closed points and then the circuit is open when the points open.

Be sure the condensor or its wiring is NOT shorted out and see if the lite comes on (when points open) with the condensor disconnected. If removing the condensor makes her spark, replace the condensor.

SUMMARY

Be sure the points are closing fully and open on high cam and ARE NOT BURNED OR PITTED OR CARBONED UP BADLY,,,,,,,theres voltage present on distributors high side at all times when ignitions on (or its a bad switch or open ballast or bad wiring to col),,,,,,,voltage on coils low side flashes on and off as distributor is cranked,,,,,,,,,condensors not bad/shorted,,,,,,,,no shorts in wires to points and no shorts in pass thru side out distributor stud,,,,,,,,coil has continuituy.

You may luck out n just need a good battery or a replaced ignition switch or a cable or ground connection improved.

Good Luck n God Bless, post back any questions and your findings and any questions.

John T Nordhoff in Indiana, retired electrical engineer who usually lurks over on the Mother Deere boards versus over here on the “dark side”.

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