MTFCA Forum

My 1914 Touring is 111 years today so I went out to take it for its "birthday" ride. It has been sitting for about six weeks, so I followed my regular starting procedure:
Set brake
Retard spark
Advance throttle a few notches
Open gas valve just before the carburetor
Open the GAV 1/2 turn
Pull choke wire out while pulling up on crank to "prime" the engine (I pull up from 6:00 to 12:00 four times)
She's ready
Switch to MAG
One sharp pull from 6:00 and "bang!" she's off and running!
Advance spark, back off the throttle and close the GAV the 1/2 turn and she's running smooth.

Today.... she started right up on MAG as always, but running rough, balking, like it's missing on half the cylinders!
I switched over to BAT... Beautiful! smoothed right out!
Back to MAG..... Almost quit running entirely! Like it's running on one cylinder! Rough, like its going to backfire, bucking..
Back to BAT... perfect!

Before I go crazy, where do I start looking here? Why would it all of a sudden act so strangely?

Appreciate any advice or step by step diagnosis to try to find the problem.

Gary

I'd check the mag. post for "crud" first.

Fuzz on spring loaded mag post ? Broke off piece of lacing wire shorting out field coil button ? That happened to me - same symptoms…

By ONE minute Steve…. you beat me by ONE minute

George House wrote: ↑

Fri Mar 14, 2025 2:47 pm

By ONE minute Steve…. you beat me by ONE minute

Now George, it's not a competition... but if it were... Steve won!!

Start engine on battery switch over to magneto put a AC voltmeter on the magpost and what is your reading. ??? ...Either there is lint on the magpost or your magneto has to be recharged if your AC voltage is not between 7 to 10 volts at medium idle.

Does it run at all points on the spark lever? The re are three, sometimes four locations set the spark lever on magneto. It should have these three points where it runs smoothly. In between those locations it might not be so smooth. Also could be points are adjusted so that some spark earlier than others. And another reason to run rough is fuel richness adjustment. however it should run as smooth on battery as as on mag unless one of the above could be causing it. See also above posts.
Norm

Funny George !!!

I had the same thing few years ago and found that the wire block had a loose connection. Ran with some skipping and once the nut was tightened, ok again.
You may look at that.

I pulled the spring loaded magneto plug and it is clean and shiny. No lint anywhere. I wiped it off and re-installed it
I opened the front of the coil box (where the key goes in) to check the internals and all the clips are tight and soldered connections are good and tight.
I tightened all thumb screws to eliminate that, but everything was good.

My "T" runs nice and smooth throughout the spark range, either on BAT or MAG. I really don't experience the "peaks" and "valleys"
Also, the fuel enrichment knob has a definite "sweet spot" that you cannot miss. a couple degrees one way or the other and you know it.


Tomorrow I'll start it and check the mag output with the voltmeter. what leads go where? I don't want to damage the magneto by shorting it out somehow.

Thank you for all the suggestions and please keep them coming! I'll check in tomorrow with the voltmeter results.

Appreciate your help and advice.

Gary

Just make sure thats an analog voltmeter. I also like to install magneto meters the suppliers sell. Oh, and that’ll be one voltmeter contact (black?) to ground and the other (red?) to the top of mag post.

Be sure your volt meter is set to AC, the red lead would go to the magneto post and the black lead to a metallic ground.... Even better go into the engine compartment and have the red test lead connect with the red wire magneto terminal on the firewall terminal block and then the black test lead would go to a metallic ground. The engine would have to be running while taking these readings..... After you have time to do your test, kindly tell us your AC voltage results on idle, and at faster moderate engine speed.

I've been there. It's lint from the bands. Honestly, that's about the only problem I ever have with the magneto since some friends and I had a "Magneto University" meeting back in 2010. Just pull the mag post, remove the lint, shine a flashlight into the hole atop the hogshead and make sure there is no lint left on the blob of solder. Re-install the mag post.

You may want to check your coils on a HCCT. This will confirm if your coils are adjusted for running on the magneto. I have Mike Kossers tool and an HCCT and have found my coils work better when tested with both tools.

As stated before, check your mag voltage when running.

I have also seen problems with the switch not making good contact on mag and or battery.

The last post may solve your problem. Coils that are set and run good on battery might now double spark on magneto which produces an early weak spark and rough running. If nothing else solves the problem I would check them.

In the initial posting he does indicate a problem running on mag after running smooth on battery... Then later on posting that the engine runs smooth on both battery and mag.. coils need adjusting, questionable,.... loose contact somewhere in the wiring. Possible... He will be looking into it soon and hopefully posting his results...... Possible ignition switch mag position contacts having bad connection?

I just got out to the garage to check the mag voltage. I used a digital voltmeter as I don't have an analog unit.

I hooked the wires red to the mag wire under the hood (porcelain plug), black on ground.

I got a free "hot start" on BAT after priming.

Meter reads 3.5V AC

That's it. And the 3.5 V stays pretty steady through all RPM ranges, from idle to fast idle.

When I switched to MAG, it all but quit entirely. Literally sounds like an old "hit or miss" engine. One cylinder fires every once in a while to keep it just barely limping.

Switch back to BAT, smooth as ever.

Bummer. How does this just happen?

(Let me clarify a previous post... when I stated it runs smooth on BAT and MAG through the spark range, I meant "until now")

Thanks for any help going forward.
Gary

Your in-car magneto needs a recharge.

I could be about 30 miles away from you, but I would be available to help you recharge your magneto.

Consider all that is spinning around inside when you start the engine each time - only takes a piece of crap to become dislodged and catch on the mag. contact - easy enough to remove, check & clean !

Gary .....Just for the hell of it, put in a new mag pickup on top of the transmission cover and start as usual.

Gary ... Any up-dates on the magneto problem ?

I’ve ordered an ANALOG volt meter, got my 1156 sockets and bulbs, and as soon as the meter arrives I’ll follow the Reagen/Patterson schematic and test again. I’ll update as I test.
Thanks for checking in!

UPDATE:

I used the analog AC volt meter with an 1156 12V bulb. Attachment directly onto the MAG plug and grounded to an engine stud.

The bulb filament exhibits a dull orange color and the voltmeter never exceeds about 3V from a "spark-retarded" slow idle, all the way to a fast idle.
Literally no change through all RPM's. I got the same reading with my digital volt meter. I am totally at loss what on Earth could have possibly happened here, but it's a bummer.

I don't know if it matters, (I think it might), but that looks like an 1157 bulb, (dual filaments). I think an 1156 is a single filament bulb. The 1157 may draw a lot more current and pull down your voltage.

Did you remove, inspect & clean the contact ??????????

It’s an 1156 single-filament. Just reflection in the photo
Removed and replaced mag post. It is spotless so I wiped it and reinstalled
Removed coil box entirely from firewall and inspected every wire/connection. Everything is tight, clean and in perfect working condition.
Got same voltage reading from mag post and firewall mag porcelain post so I know the wire is good.

Thanks for the help/advice/ideas….

This is what you need.
viewtopic.php?t=45508

Have you tried seeing how much end play your crank has?

Electrics are not my strong suit, but I get by.
If what I am about to say is incorrect, I hope our smarter T people will correct me.

Seeing your testing hits me as screwy.
I thought the light bulb test & voltage output test were TWO separate tests. You have them combined in series.

The light bulb test by itself Looks for a visual condition by the brightness of the bulb. @ idle the bulb should light ok. As the rpm increases, the bulb gets brighter to near blowing out.

The ac voltmeter test by itself reads mag output by voltage readings. Idle should be 6-10 volts. As you raise the rpms voltage rises. High speed 18-30 volts. Furthermore, your meter is in the wrong scale for an accurate voltage reading. It should be 50V max. You dont use a 150# truck tire gauge to test for 30# on a modern car tire. Such gauges are designed to be accurate in the middle third of the gauge.
You might try testing again separately.

Even with your testing method, the 12v light bulb is well lit. How can that be only 3V? I think the bulb is bringing down the voltage reading by its presence in the circuit or the meter is way off. (I do have recent experience with an inaccurate Chinese ammeter.)

By example: I have a home made rectifier on my 14 to convert the 30V mag output to charge a 12V battery @ 3 amps.
The bulb does not light @ idle, yet the motor still runs very well on mag. @ road speeds It glows bright. I had to use both filaments or the light would burn out.
Testing without the rectifier in the circuit, mag post only, shows 12V @ idle & 32V @ hi speed.

speedytinc wrote: ↑

Wed Apr 02, 2025 4:07 pm

Electrics are not my strong suit, but I get by.
If what I am about to say is incorrect, I hope our smarter T people will correct me.

Seeing your testing hits me as screwy.
I thought the light bulb test & voltage output test were TWO separate tests. You have them combined in series...

The procedure, as described by Ron Patterson in an old forum posting...

"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."

It would appear that the OP, Gary W, did it correctly.

I have no idea, but do carbon tracks in the coil box act different on mag vs battery?

Gary.... Has your magneto ignition power source problem been resolved?

Secondary insulation problems might be worse on Mag due to higher peak voltages.

Really Pat ???? Please explain. Thanks

The magneto can supply higher primary voltage than than the battery can. That might allow higher secondary voltage to be developed, which might provoke insulation break down, especially in damp weather.

Have you looked inside your timer?

Hey,.... Save that one for April fool's Day next year.

"You have them combined in series."

Should be in parallel.