Farmall A magneto issues

I have a 1945 farmall A with a H4 magneto, when I got the tractor someone had disconnected the wire from the kill switch and connected it to a key switch. I reconnected it to the kill switch and that worked for a while, but then the kill switch quit working. I was planning on replacing the kill switch but in the meantime I was going to reconnect the wire to the ignition switch to make it easier to shut off. Well I stupid like connected it to the ignition post on the key switch and turned it on, which fried something in the magneto (probably about a week after rebuilding the magneto I will add). Today I replaced the coil, condenser and half of the points, and I cleaned the other half of the points and then set them. It has ignition when you take the top cover off and connect, or try at least, a spark tester to the coil, it also usually has fire on the coil wire, sometimes it wouldn’t but that could have been because it wasn’t making good connection, but it does NOT have fire on the spark plug wires, no matter what. The distributor and rotor look ok (I replaced the rotor when I rebuilt the magneto). I can’t figure out what’s going on.

This post was edited by bdoss2006 on 09/29/2022 at 05:14 pm.

When you apply battery power to a magneto coil it usually fries it and the magic smoke escapes and you usually need a new coil for it.

I replaced the coil though, but it still doesn t have fire on the plug, it does in the coil wire though, but it might look a little dim

How much spark is coming from the coil? It needs at least 1/2 inch to make it
through the rotor and cap.

Is the impulse spring working?

What is 'replacing half the points'? Chances are when power was fed to the
mag, it may have arced the points, damaging the surface of both contacts.

I suspect replacing the coil is quite an in depth procedure. Is the rotor
pointing to a distributor terminal when the points break? Have you tried the
old rotor or carefully compared the old to the new? Everything is aftermarket
now, very common for there to be differences in manufacturing, some subtle,
some completely wrong!

I guess I'm not understanding the purpose of an ignition switch, connected to battery power, on a tractor with a magneto.
What kind of a set up do you have there?

I ll have to measure the amount of fire, I assume the impulse spring is working, it ran fine before I connected power to it. By saying I replaced half the points I meant I replaced one side. The other I replaced when I rebuilt it. I sanded both sides though.

(quoted from post at 17:58:18 09/29/22) I replaced the coil though, but it still doesn t have fire on the plug, it does in the coil wire though, but it might look a little dim

Click to expand...

Is the rotor timing correct?

https://farmallcub.com/rudi_cub/www...Magnetos/GSS-5035 Service Manual Magnetos.htm

Page 51 in the GSS-5035 Blue Ribbon Service Manual linked above.

well here s an update, I kept fooling with the distributor cap and rotor and finally got it to have ignition on all 4 wires. I think it should have enough to start, but it won t. I don t think it is getting gas. I turned the engine over then took the spark plug out and didn t see any gas. I don t know how it couldn t be getting gas though, the line is not stopped up and I took the carb apart thinking it might be dirty but it looks fine. What happens if you move the magneto when you take it apart? Of course when the number cylinder fires it should be at top dead center. But if the magneto was moved. It could fire without it at top dead center. How does that work?

The timing Mark is on the flywheel. You need to remove the inspection
plate under the torque tube then use a flash light to look toward the
engine. The mark on the flywheel says some thing like D C 1 4. The other
mark is a line cast into the flywheel cover. Be sure number 1 calendar
is on compression stroke then line those two marks up. Install the
magneto fully retarded with the rotor coming up on number tower on the
distributor cap. Rotate the magneto until the impulse trips then tighten
the bolts. You should now be timed correctly.
Dave

I think the kill wire from a Magneto is connected to ground that
shorts out the points.
You don't apply power to a mag.
The ignition switch on a lawn mower has a terminal that connects
the ignition module to ground.
All other terminals have power on them..
I doubt if your ignition switch has a grounding terminal.
My Farmall C has a separate switch to short out the mag.
The other switch is to apply power to light and alternator.

If having a key switch is your thing, you can do that.
Use a switch from a lawn tractor and hook the mag
wire to the single M or G spade. But the switch
housing must have a good ground for it to work.

(quoted from post at 22:00:21 09/29/22) How much spark is coming from the coil? It needs at least 1/2 inch to make it
through the rotor and cap.

Is the impulse spring working?

What is 'replacing half the points'? Chances are when power was fed to the
mag, it may have arced the points, damaging the surface of both contacts.

I suspect replacing the coil is quite an in depth procedure. Is the rotor
pointing to a distributor terminal when the points break? Have you tried the
old rotor or carefully compared the old to the new? Everything is aftermarket
now, very common for there to be differences in manufacturing, some subtle,
some completely wrong!

Click to expand...

well I took the carb apart and it looks fine (it is just about a year and a half old) I put it back on and it wouldn t even fire on starting fluid. I tried timing the magneto, I think I got it right. It still won t work though. I don t know if it doesn t have enough ignition or what, but pretty much everything in the magneto is brand new or just replaced a month or so ago. I checked the compression in the number 2 cylinder and it was 75 which seems a little low but I don t think that is the problem considering it was running fine.

(quoted from post at 22:00:21 09/29/22) How much spark is coming from the coil? It needs at least 1/2 inch to make it
through the rotor and cap.

Is the impulse spring working?

What is 'replacing half the points'? Chances are when power was fed to the
mag, it may have arced the points, damaging the surface of both contacts.

I suspect replacing the coil is quite an in depth procedure. Is the rotor
pointing to a distributor terminal when the points break? Have you tried the
old rotor or carefully compared the old to the new? Everything is aftermarket
now, very common for there to be differences in manufacturing, some subtle,
some completely wrong!

Click to expand...

well I took the carb apart and it looks fine (it is just about a year and a half old) I put it back on and it wouldn t even fire on starting fluid. I tried timing the magneto, I think I got it right. It still won t work though. I don t know if it doesn t have enough ignition or what, but pretty much everything in the magneto is brand new or just replaced a month or so ago. I checked the compression in the number 2 cylinder and it was 75 which seems a little low but I don t think that is the problem considering it was running fine.