Rough on magneto

[Bill67]

Hi. Last week I posted a question about my magneto not working. Several people gave advice and I have it working; problem was in the switch. (Thanks for all the help).

I just took it for a short ride (close to a mile). It is definitely running more rough on magneto than on battery. Any ideas?

1925 touring with 1919 engine. Thanks for any advice.

[speedytinc]

Did you check the output voltage??
AC analog voltmeter. Low voltage behavior.

[Bill67]

When we got it running on magneto, we put an analog volt meter on the post. I revved it up and it went up to 17 before I shut it off.

[speedytinc]

Does it run rough @ the higher speed that you got the 17V reading? What is the voltage reading during the rough running?
Point being @ idle & low RPM's, the voltage could be too low to run well.(weak magnets)
You polished the contact points & retensioned the contacts in the switch & the wire connections are clean?
I dont remember if your coils were stated to be in good tune.

[TWrenn]

Hi. Last week I posted a question about my magneto not working. Several people gave advice and I have it working; problem was in the switch. (Thanks for all the help).

I just took it for a short ride (close to a mile). It is definitely running more rough on magneto than on battery. Any ideas?

1925 touring with 1919 engine. Thanks for any advice.

Bill I bet it's your switch. I'm attaching 2 pics..my Fordor runs great on batt, and only on mag for about 2 trips after I open it up and tinker with it. It's a repop. I went back to the original after Cleaning up the contacts and making sure they are "firm". The repop, with the yellow circle, shows how poorly the contact is from the male portion into the little female depression contact. I am sure that's what the problem has been.

[Ron Patterson]

I have spent most of my adult life working on Model T Ford electrical problems.
Please do this test exactly as described, provide the results, i will interprete the results and tell you how best to procede.
Go to your local auto parts store and buy a #1156 bulb. This is commonly used as a back up light bulb in modern cars. This bulb will come close to simulating the load of a typical Model T coil. You may want to pick up a socket for it too and put some wires on it to make a regular test light out of it.
Connect the bulb across the magneto output and ground while you running the car on the battery with the emergency brake pulled all the way back and set. Using an analog voltmeter check the AC voltage across this bulb as a load.
Provide the following test results back to me via email:
AC Voltage reading at engine idle:
Lamp Brightness at engine idle:
AC Voltage reading at engine moderate speed:
Lamp Brightness at engine moderate speed:
AC Voltage reading at engine high speed:
Lamp Brightness at engine high speed:
Ron Patterson

[Bill67]

Thank you for the answers. As soon as I do the tests, I will get back to you.
Bill

[Norman Kling]

Could be the switch is still in trouble. Another thing I was thinking of is the coils aren't set correctly. Or if you have a 12 volt battery and the magneto voltage is low, it might not run smoothly until the engine picks up speed. Anyway, when on battery, the electricity will begin to flow through the coil as soon as the rotor makes contact. So if the coils are not exactly the same they will spark with a continuous spark as long as the rotor is in contact. However with magneto, the current will build as the AC rises for each cycle of the magneto. So somewhere in the middle of the rotation after the contact is made, the current builds up to the spark. If one coil sparks earlier than another coil, it could cause rough running. All the coils should be set to draw 1.5 amp when it is sparking. If they are all set the same, then it should run better on magneto than on battery and as you pick up speed it will actually advance the spark a bit because of the higher peak of the sine wave.
Norm

[TWrenn]

Orrrr...you could put one of these on your car and then you'll always know what your mag is doing!

[Bill67]

Thanks to all who have answered. One coil is a new rebuilt, but the other three have been in there since the 80s (but not being driven). I have no idea what they are adjusted to. It sounds like a good idea that I should pull them and have them all checked.

[TWrenn]

Thanks to all who have answered. One coil is a new rebuilt, but the other three have been in there since the 80s (but not being driven). I have no idea what they are adjusted to. It sounds like a good idea that I should pull them and have them all checked.

That certainly can cause unsatisfactory performance, however in my not so scientific mind, I would think if that were the real case, then the engine wouldn't run very well whether you're on battery or mag. Others may have a better idea, and I will add that to the learning experience!

[TXGOAT2]

Important: Have your coils refurbished and adjusted, then test the mag as Ron directed. Be sure the wiring and switch are in good order and that the timer is working correctly. The car should run better on Mag.

[Norman Kling]

Ron Patterson is an expert on coils and magnetos. His test will confirm whether the magneto is working properly.
Norm

[TRDxB2]

Hi. Last week I posted a question about my magneto not working. Several people gave advice and I have it working; problem was in the switch. (Thanks for all the help).

I just took it for a short ride (close to a mile). It is definitely running more rough on magneto than on battery. Any ideas?

1925 touring with 1919 engine. Thanks for any advice.

You said - It is definitely running more rough on magneto than on battery.

I interpret this as saying it is running rough on battery as well as magneto. True?

If so, the first thing is to resolve running on battery (its less complicated). The common denominator for running on MAG & BAT is the ignition switch & coil units. So once these are operating correctly you can start investigating MAG issues. You'll never resolve MAG issues with a faulty switch or coil unit.
If you can't feel the ignition switch index into position when switching the key to MAG and/or BAT, it is likely the switch is still the issue. At first you were unable to run on MAG at all until you raised (bent) the contact into position. I am suspecting that the back cover plate of the switch may be slightly warped. Running the bottom over sand paper might help. Or getting a new backing plate.

If the switch is making good contact , then the coils need to be checked. Since you said in the previous post " I’ve owned a 1925 touring (1919 engine) since 2000, but just recently got it in running condition. It was built in the mid 1980s by someone else". It is likely you have coil issues.
Suggest you first follow pages 3 & 4 - and if that does help you need Ron Patterson to help with the coils

Model T Adjustment 3_7_21.pdf

(6.47 MiB) Downloaded 58 times

Down load this its the 1925 service manual 315 pages - still applicable to1919
https://www.cimorelli.com/mtdl/servicem ... mcolor.pdf

[speedytinc]

Actually, AFTER you determine the mag's condition, you can move on to the other issues by ruling out or ruling in.
I would not expect your poor running issues to only one thing. You pick at each possibility until you have a great running T.
I dont doubt your coils need tuning on an ECCT, there are timer issues, coil box connections, switch & wiring, carb issues, etc, etc........
but the mag output test is an easy thing to confirm.

[John Codman]

I agree with those who feel that your coils should be checked out, but I doubt that coils are your major issue. The maximum voltage input to the coils on BAT is about 6V. On MAG it should be much higher, plus the electrical load to operate the oscillators (buzzers) is gone. If you can establish that the magneto is putting out the proper voltage at it's post, the problem has to be between the MAG post and the coils. Somebody earlier posted that you should use an analog meter. I cannot think of a reason why a digital voltmeter wouldn't work just as well. Perhaps I'm missing something; I am willing to be enlightened.

[Bill67]

Thanks to all again

I think I’ll try lightbulb test next.

Being new to this, I feel like I’m chasing problems in circles (which I assume is normal). I won’t give up and when I have new information or results, I’ll post them.

[speedytinc]

I agree with those who feel that your coils should be checked out, but I doubt that coils are your major issue. The maximum voltage input to the coils on BAT is about 6V. On MAG it should be much higher, plus the electrical load to operate the oscillators (buzzers) is gone. If you can establish that the magneto is putting out the proper voltage at it's post, the problem has to be between the MAG post and the coils. Somebody earlier posted that you should use an analog meter. I cannot think of a reason why a digital voltmeter wouldn't work just as well. Perhaps I'm missing something; I am willing to be enlightened.

Have you tried using a digital meter around a running T?
What you are missing is that the coil ignition system wacks out even top quality digital volt meters.(even Fluke's)
You will get readings of random garbage.

[speedytinc]

Thanks to all again

I think I’ll try lightbulb test next.

Being new to this, I feel like I’m chasing problems in circles (which I assume is normal). I won’t give up and when I have new information or results, I’ll post them.

It can appear you are chasing your tail until you rule out & fix the multiple issues that are occurring @ the same time one by one.
For example, you may have a weak mag, coils needing a tune, a fowled plug & a misadjusted carb.
The maddening issues occur intermittently & are hard to pin down.
The problem chasing is part of the fun. Before you know it, your T has lots of horsepower & is a joy to drive.

[nicklm]

I had a similar issue when our 26 motor was rebuilt. Ran well on battery and rough on mag. One of the terminals wires on the block on the firewall was loose. Missed some on mag but better on battery. After tightening, it ran well on mag. It was a simple check to tighten all the screws for a good contacts, then if it does not work, go to the other suggested options.
Nick

[Norman Kling]

Nick reminded me of something which I ran across in the past. If you have a steel firewall on the car, sometimes the screws on the terminal block are a bit too long and bottom out against the metal.
Norm

[TWrenn]

Nick reminded me of something which I ran across in the past. If you have a steel firewall on the car, sometimes the screws on the terminal block are a bit too long and bottom out against the metal.
Norm

Ha ha...took the words right outa my keyboard while reading the post above yours!! An absolutely often overlooked item!

I even forgot about it myself whilst offering my two cents worth!