MTFCA Forum

For whatever reason, the car runs great on mag except when you stop and fully retard the spark! Then it stalls. When on battery, it will stay running with the spark fully retarded. This is something that just started. What do I check? Merry Christmas and thanks!

Weak mag, if you read up on it you can recharge the magnets in the car.

It has a new mag. It's very strong.

When you run on battery, you have 6 volts DC at the coils at all times. It depends on when the rotor comes in contact with the segment for the timing, however, when you run on magneto, the AC voltage begins to climb as your magnet passes the magneto ring coils and when the voltage builds to peak, it fires. So when you have the timer fully retarded, your peak comes a bit later and your rotor passes the segment before it sparks. So, don't retard all the way when you are on magneto and if you try to start on magneto, advance the lever a notch or two when you crank. Note, experiment to find the best spot for starting on magneto being very careful to be sure it does not kick. When you find that spot, always set the lever there if you try to start on magneto.
Norm

Norman has given good advice

I'll amplify one thing, once it's running, there is zero reason to retard the spark "all the way". In fact, few to no cars can be started on mag with the spark "all the way" retarded. They will all require several notches of advance for the timer to be in proper location to the pulse created by the sine wave of the mag. If they will start on Mag, with full retard, you likely have the timeing wrong. I don't think this is the case, since it stalls when fully retarded on Mag. Frankly, it sounds perfectly normal. A little more throttle and it will likely carry through and run, but that's really not the point.

and one tweek to Norm's advice: unless your timing is wildly out, or something is terribly wrong/shorted in your ignition system the risk of a "kick" or backfire when starting on mag is very remote. I don't get that either of those things is true from your post.

As with all Model Ts, it is imperative to have the timer adjusted for correct retard. I say that as a general statement whenever discussing timing/starting. If you are certain of it being correct...proceed...if not, then stop and correct. Now.

Steve Coniff and Ron Patterson wrote a great paper on this and is worthy of being read and understood by all Model T owners: http://www.funprojects.com/pdf/Model%20 ... iticle.pdf

Norman Kling gives a good description of how to find the sweet spot for starting on Mag, on July 2, 2014...read it here: http://www.mtfca.com/discus/messages/41 ... 1404331644

that's where it should start, and that's where it should be set to idle

Johnathan
Have you checked the initial timing setting?
The initial timing should be set at 15.5 degrees ATDC with the spark lever fully retarded.
Please see the link above to article Steve Coniff and I wrote on Model T Spark timing and how it was intended to operate.
The article also addresses the correct way to hand crank start the Model T Ford on magneto.
If you have any questions give me a call.
Ron Patterson
859-881-1677

Word of caution; be aware of free (unexpected) starts when making adjustments to the timer with the key set on “BAT”.

The timer is very close to the fan and I do not recommend doing any work to the timer if there is a potential for the car to start for that reason.