More JD 70 Pony Motor Frustration

ROSchell

Member
Okay, so I replaced the switch, points, plugs and wires, and coils after burning the coils out. Fired it up about 4 or 5 days ago, and it ran like a top. I've been starting it every day to make sure everything is still good. Today I went to start it, and it started, and then died out and wouldn't start. It was out of gas. I found that there was a drip at end of the gas line under the hood. Took the hood off and replaced the hose with a new one that appears to be the correct size. Fired it up and thought all was good. Put it back together and before I could get the diesel engine started, the pony motor died out and wouldn't start. It still gets spark to the plug, but it seemed that the front two plugs were wet. I didn't check the back two because they are so hard to get at. I took the front ones off and blew them out, and tried it again, but they still wouldn't fire. Hooked up a cable from the battery to the distributor, and it started. I unhooked the cable from the battery, and after the motor ran for a bit, it was just like you turned the switch off again.

Is there something in the new switch that shuts the voltage down if it gets too hot? I ask because sometimes I can smell hot wires and I'm not sure why that is. I did have to replace the hot wire from the switch to the distributor because it had gotten way too hot when I initially burned things up. I'm certain I hooked the new switch up right, as I had both there and did it wire by wire. It just seemed that it would die out and not start, but after you messed around for a few minutes, it would fire back up, almost like once the switch cooled down, you were good again. Also, what gauge wire should be used from the switch to the distributor terminal? It seems like I used the same size as what I replaced. I'm just so frustrated because I thought I had it fixed and running good and now it's giving me problems after just a few days.

Any help is greatly appreciated as I don't know where to turn since there's nobody around anymore that knows much about these pony motors.

This post was edited by ROSchell on 06/02/2023 at 08:27 pm.
 
I believe there is suppose to be a resistor on that wire that drops the voltage on those coils because they are very easy to burn up if there is too much voltage. 6 volts from the battery is too much. You can probably guess how come I know that.
 
I converted my 70 diesel to electric start years ago and dont miss the pony motor one bit! One engine is enough to worry about. I kept the pony in case
I ever sell the 70 so it can be put back to original if the new owner desired.
 
So, prior to leaving for work this morning, I quickly checked voltage to the distributor and got about 1.4 volts. Yesterday before the troubles, it was at about 4.5 volts. Switch is new from Steiners. Where could the voltage be going?
 
(quoted from post at 13:25:51 06/03/23) So, prior to leaving for work this morning, I quickly checked voltage to the distributor and got about 1.4 volts. Yesterday before the troubles, it was at about 4.5 volts. Switch is new from Steiners. Where could the voltage be going?

I would also add that the voltage seemed to come and go after our troubles started. I would check it and it would be 4.5, then it would die out and not start and it would be down to 1.4. Maybe we bumped the wire on the switch and it came into contact with metal when we replaced the gas line or were messing with the tach cable. Could that do it??? Things were pretty tight in there and I had to bend the connection from the switch to distributor so it wasn't touching the bar that goes right behind the switch.
 
(quoted from post at 04:14:20 06/03/23) I believe there is suppose to be a resistor on that wire that drops the voltage on those coils because they are very easy to burn up if there is too much voltage. 6 volts from the battery is too much. You can probably guess how come I know that.

Actually, the ignition resistor is on the back of the ignition switch, a ''coil'' of nichrome wire.
 

Yes, the resistor is on the back of the switch. It's a new switch, used maybe 20 times now as I've been working on it. I know it's common nowadays for these switches to go bad, but how do I know if it's the switch or resistor? If the resistor burns out, you would have full voltage, correct?
 
My guess is that the contacts on the back of the switch are touching something to short it out. Could be what you are smelling. Very tight quarters behind the dash and can easily be shorting out. Usually touches the throttle shaft that runs from the right side of the tractor to the left side.
 
You may want to confirm that you have a good ground path to the battery. If the battery is grounded to the battery box, you might not have a good ground path as where the box secures to the rear end casting is notorious for rusting and corroding. Attaching the ground wire to the casting provides a good solid ground.
 

Posted by buickanddeere: "Use an ohm meter to check the resistance of the resistor . Open means no connection , no current."

You'll have to excuse my ignorance as I'm not too sharp when it comes to electrical issues, but if the resistor was bad, wouldn't it allow the full amount of current through it? I've read where some say to remove the resistor completely as it will allow more voltage through to the distributor???

This post was edited by ROSchell on 06/03/2023 at 09:17 am.
 
I know you are saying you are ..no electrical guru.. but
youre thinking about if a resistor that burns out it will
provide full voltage is incorrect. Look at the item in the
link that is the resistor, it is just a coiled continuous
wire as another poster suggested. If it burns out or
becomes open it will not conduct any electricity. Not
saying this has anything to do with your problem just
helping your electrical knowledge out. I suspect the
difference between the voltages you measured had to
do with the points being opened or closed. My guess is
that you did not get a connection tight somewhere
when you were swapping parts. Another thing could be
that the new condenser is bad, very common problem
these days.
Example resistor
 
(quoted from post at 18:45:53 06/03/23) I know you are saying you are ..no electrical guru.. but
youre thinking about if a resistor that burns out it will
provide full voltage is incorrect. Look at the item in the
link that is the resistor, it is just a coiled continuous
wire as another poster suggested. If it burns out or
becomes open it will not conduct any electricity. Not
saying this has anything to do with your problem just
helping your electrical knowledge out. I suspect the
difference between the voltages you measured had to
do with the points being opened or closed. My guess is
that you did not get a connection tight somewhere
when you were swapping parts. Another thing could be
that the new condenser is bad, very common problem
these days.
Example resistor

Okay, thanks for clearing that up. So the coiled wire is the resistor. If I remember right, the wire that goes to the distributor hooks on one side. Does anything hook to the other side of the resistor? If you were going to eliminate it, would you just unscrew the resistor on both sides and remove it and leave the ignition wire in the same spot? Not that I'm going to do this because with a new switch, I don't think the resistor could be burned out as I didn't have the switch on for long periods of time. And I don't want to take the chance and burn anything out again. Again, sorry for not knowing this, but what is the little battery looking piece for? Is that also a resistor for lights???

mvphoto106324.jpg


This post was edited by ROSchell on 06/03/2023 at 12:35 pm.
 

Okay, so I got home today and before I tested voltage at the distributor, I moved the throttle ahead. It tested at 4.5 volts, like it did previously. I know, I should've thought to test it before I moved it, but I didn't. I removed the dash and re-tightened and repositioned the wires closest to the throttle shaft. I tested again, and it was at 6 volts. Perfect, I thought. Put it all together and re-attached the dash and we were back to 4.5 volts. It fires right up at 4.5 volts, but it must still be losing voltage somewhere. It's just too hard to get at, so I'll keep an eye on it and keep measuring voltage, and if it does it again, I'll maybe have to remove the hood and see if I can get better access with that off.

I'm keeping my fingers crossed!!!!
 
Going through the resistor it should be reduced from 6 volts to 4.5 volts, so you are ok. On some models the starter button mounted on the starter had a side terminal so that when the starter was turning you had a straight 6 volts going to the coils and when the button was released it went to 4.5 volts. Suppose to extend the life of the coils. Don't take this as a recommendation, but I bypass the resistor and give the coils 6 volts all the time. Just need to make sure the red dash light works and don't leave the switch after the pony engine starts. You can still harm the coils at 4.5 volts if the switch is left on, just takes longer.
 

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