620 won't run through ballast resistror...WHY????

~Are you sure the coil is a 6 volt coil? Is the voltage written on the coil can? [if that coil is actually a 12 volt internal resistor coil it won't function at 4.3 volts period. If you have an ohm meter on your VOM, measure the resistance between the + & - small terminals on the coil, if under 2 ohms you have a real 6 volt coil, if over 3 ohms it flat won't work with that external ballast resistor.

~You might want to put the voltmeter on the coil's ballast resistor side then monitor the voltage as you switch from 12 volt [jumper] to ballast resistor supplied voltage.. The coil's supply voltage should get higher with the tractor running due to the charging system coming on line & the fact that the points should spend less dwell time at ground so the current draw should be less. [with it running the coil's supply voltage should be a little higher than the 4.3 you measured statically]

~As another test you might try running your 12 volt jumper wire to the coil side of the ballast resistor [see if it runs that way as that will test the wiring from the ballast resistor to the coil],,,then with it running simply move the jumper wire to the ignition switch side of the ballast resistor, if it still keeps running suspect the ignition switch has excess resistance [common] or the wiring from the ign switch to the ballast resistor has excess resistance.

~If the coil's supply voltage is 5 volts or over running I would suspect either a bad coil, or the condenser isn't functioning, or the distributor has a poor ground, or even fouled spark plugs.

~If nothing stands out per above you might have a mismatched ballast resistor for your coil. The ECH 1CR13 ballast resistor from NAPA [about $14.00] seems to work good with most 6 volt coils on a 12 volt system & might be worth a try. It's real hard to accurately measure the resistance of a ballast resistor due to the change in resistance from cold to working hot.

~It might be as simple as a set of partially fouled spark plugs & the higher 12 volt coil supply voltage is enough to change the coils rise time to overcome the fouling & still supply enough KV to jump the plug gap. [it might pay to try new spark plugs]

~If you can find another coil to try it might stop a lot of guessing & say yes or no to the coil as a source of the problem.

~This is a strange & unusual problem so can you tell us when the problem started? Did it just start all of a sudden? Or did you buy the tractor with this problem?

~Let us know what you find when you get it repaired?

I'm also impressed with Pertronix 3 ohm coil which needs no ballast resistor - but $30 price does take ones breath away at first. My 59 chevy has never run so smooth nor idled without missing like it does now - I'm looking for a distributor for my 43 A so that I can 'Pertronix' it too, with or without the solid state points part.

If $30 for a coil takes your breath away, consider the $55 for a starting engine coil, and you have to use two !

I wish there was an electronic unit for that engine.

Frank-in-Tallahassee
70D // 855

Take care, John T up North of you

You know, I've seen those same 4 coil set-ups, but I always wondered why they didn't just use two coils and a "Y" connector to run the two plug wires to the same side plugs since that's the way it runs from the originals. Or is it that there wouldn't be enough juice to fire the pressurized plug ? So are the pony coils actually bifilar wound, like two coils in one case ?

I'd like to talk to you more about customizing an electronic box. I just think if the ponies had a sharper spark it would help all the way around. Even if it meant going to 12 V it wouldn't be all bad. I think it might help get a round the posible fouling that comes from engines that are most often started cold.

I'll do some internetting and maybe start another thread up above and you can give me some advice.

Thanks again !

Frank

Measure the DC resistance of the coil primary and the ballast and Im afraid the ballast will be considerably higher, when it should be near the same or slightly less????? ????? ???? The coils primary resistance should be near or slightly less than 2 ohms if its really a 6 volt unballasted unit.

On a 12 volt tractor that uses a 6 volt coil and a ballast resistor which is equipped with a ballast by pass starting circuit fed off the extra lil terminal on the side of the starter switch, they are supposed to start (when engine cranking) with full battery voltage on the coil, and then the coil voltage drops to 6 to 8 (depending on ballast size) volts (not low like 4.3) because the voltage dropping ballast is back in the circuit.

Now, why it wont run after started if you put 6 volts on the coil is a bit tricky. If its really a 6 volt un ballasted coil, 6 volts across it should allow sufficient current flow through it and the points to fire the plugs. I assume the ballast is fed 12 volts from the ignition switch, and its output side leads to the coil. The output side of the ballast or the high side of the coil (same electrical point) should have the extra start by pass circuit wire up from the start switch which is battery voltage ONLY when starter is engaged.

Here are some things in question as to why it wont run with 6 volts on the coil:

1) Youre sure its a 6 volt un ballasted coil?? if it had an internal ballast and its polarity were wired wrong, it causes a weaker spark. Resistance should be near 2 or less.

2) What ground are you running, pos or neg, and is the coil wired the same????? ? i.e. if pos grnd as original, the coils + goes to the distributor.

3) When you hot wire jump around the ballast, how are you doing that???

4) If you jumper wire around the ballast direct to the coil from the ignition switch output with it on, whats the voltage on the coils high (non distributor) side when points are closed ????? ????? Im looking for any internal switch resistance via this test.

and with the jumper on will it start and continue to run????? ? (dont run it very long) If its really a 6 volt coil, it should start and run that way, but the coil will get warm as its drawign more current than designed for.

5) Do you suspect the ignition switch?? They can go bad and create an internal resistance wherey by they may show correct voltage (with a good voltmeter) but under a load drop voltage causing low coil voltage.

Heres some other things to try:

Try a direct jump hot wire from the battery (by passes any bad switch) to the ballast input and see if she starts and runs. If it does, I suspect the switch. If it dont, the ballast could be too much resistance as originally suspected.

If she wont start that way, run the direct hot wire from the battery to the coils high (non distributor) side input and see if she starts n runs. If so but she wont via the switch, again the switch may be bad.

NOW, place a jumper wire around the ballast (to by pass it) and see if she will start either if fed from the switch (original wiring) or hot wired to the ballast high (non coil) side. Then once shes running, remove the ballast by pass wire and if she then dies, I suspect the ballast is again too much resistance.

That should be enough to get troubleshootign started, so give her a whirl and see what happens and post back the coil and ballast resistance and the voltage measurements and polarities and hopefully we can get her going. I still question the coil and ballast resistance and possibly a bad switch or switch wire might be a problem. Also, perhaps if the points or condensor were bad, it might cause a situation where 12 volts makes her run, while 6 (especially 4.3) will not. Take a look at the points and check the gap plus clean them if gray oxidized or replace them if burned or pitted or carboned up badly. You might also remove the plugs and with their wires attached and them up aghainst the frame, try the above by passes and tests and see if and when you get or dont get a good blue spark across their gaps.

Good Luck God Bless the USA, please pray for our troops. Ol John T Nordhoff in Indiana

Let us know. John T