Re: 1950 M ignition starting problem

Posted by John T on June 26, 2006 at 12:18:59 from (66.244.90.5):

In Reply to: 1950 M ignition starting problem posted by m.r.vmax on June 26, 2006 at 08:43:14:

mr, FIRST OF ALL the only circuits on a 12 volt tractor whereby theres any additional coil voltage WHILE CRANKING are circuits that have BOTH an external Ballast Resistor PLUS a Ballast ByPass (while cranking) switch n associated circuitry, either say an extra I terminal on an electric solenoid or some mechanical push start switches having the extra small I terminal (mostly on Deere mechanical starter switches, I doubt you have one)

Since you have whats called an internally ballasted full 12 volt coil, there can be no provision from a solenoid I terminal etc whereby you could even get additional voltage on the coil when cranking such as the externally ballasted systems can achieve when they start on 12 volts and then run 6 volts on a 6 volt coil.

NOW THAT WE GOT THAT STRAIGHTENED OUT we must look at other causes for your problem.

You need to verify the feed to the coil is from a correct switch and on its correct terminal (typically labeled IGN)) so when switched to ON and INCLUDING when the engine is being cranked to start, theres hot battery voltage being applied to the coil AT ALL TIMES i.e. place a voltmeter on the coils high input (NOT to distributor) terminal and when the switch is ON and including when the engine is being cranked, there should be hot battery voltage. NOTE when cranking the battery voltage normally drops, but if the battery or starter etc is bad it can drop to excess causing a weak spark n hard starting (that may be your problem)

As noted below maybe theres a hidden series Ballast Resistor lurking somewhere, it would be after the ignition switch and ahead of the coil, and if its in place youre dropping too much voltage before the coil causing a weak (especially when cranking) spark. If the coil is a true full 12 volt rated internally ballasted unit DO NOT USE ANY OTHER EXTRA SERIES BALLAST it causes too weak a spark.

Another common problem could be worn resistive ignition switch contacts. If so, theres resistance across it which drops voltage causing (especially when cranking) a weak spark, To test for that simply "Hot Wire" the coil by running a temporary jumper wire from a hot battery voltage source direct to the coils high input side n see how she starts then?????? If she starts n runs fine hot wired BUT NOT via the ignitions switches IGN terminal feeding the coil, the problems a bad switch or bad or shorted wiring from the switch to the coil.

Place a voltmeter on the coil and with the ignition points closed (which they usually are) theres should be near full battery voltage of 12.6 on the coil and if not check the switch (for voltage drop) and wiring form it to the coil.

If none of the above is the problem, its time to see what the battery voltage does when cranking, cuz a bad battery or starter or switch or cable or ground or connection problem may be causing low voltage on the coil when cranking, thus a weak spark. Place a voltmeter on the battery n crank her over n see what it reads. Depending on the starter n engine n battery n temperature etc etc it may drop to say 10 volts, but if it drops to like 9 or below its one of the problems mentioned which is reducing the coil voltage drastically causing a weak spark. Similar to the above a voltmeter on the coil can give the same results.

Looks for signs of cable arcing or where the ground cable is attached and to be safe I would remove, clean n wire brush, n reattach each n every battery n ground n starter n solenoid connection then try it !!!!!!!!!!!

A bad starter can draw excess current and drop battery voltage to excess, does the starter get hot or smoke or have that tell tale burned electrical smell???

SUMMARY: Check the coil n battery voltage when cranking,,,,,,,,,look for a hidden Ballast Resisitor,,,,,,,,,,,,check the ignition switch for voltage drop (hot wire test) and if the coil is being fed correctly from an IGN terminal thats HOT BOTH when ON and while cranking,,,,,,,,,,,,,insure the coil is a true full 12 volt rated internally ballsted unit,,,,,,,,have the battery load tested,,,,,,,,check ALLLLLLL battery cables n terminal ends n grounds n other solenood n starter connections CUZ A BAD GROUND OR CABLE OR CONNECTION CAN DROP ESCESS VOLTAGE ESPECIALLY WHEN CRANKING heck maye all you have is a bad cable or connection or a weak battery?????? FINALLY check the starter cuz if its bad it can drag the battery voltage down to excess when cranking causing a weak spark.

Theres more possibilities but I gotta get back to the hay field, good luck n God Bless, let us all know

John T

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