Which is best to run on battery or Mag. I realize when switched to battery the coils are energized and worry that might burn them out. Is this the right assumption?
If the engine is running on either, no harm to the coils. Just don't leave the key on with one of the coils buzzing and the engine off. After a time, that coil will get hot and may end up ruined, possibly messing up the coil box with tar.
Battery is great for starting the car, but once started, you should switch over to mag. The coils are happier on mag and overall your car will run a little better. It's not a huge difference though - some folks have run on just battery for long periods of time because they had an issue with their magneto. You don't really have to worry about burning the coils out unless you are going to crank the car - when you turn the switch on and hear a coil buzzing, you shouldn't let it buzz any longer than necessary to get the car started - the contacts are wearing while the buzzing is happening.
if you have a strong mag its a no brainer, when switched over to mag it will run much better
Don't the coils have to be set up right, to run their best on the mag? If not set up right, they can run decently on the battery, but poor or not at all on mag. I ran my car for 10 years on battery because it wouldn't run at all on mag and all that time I didn't think the mag was working. Switched to a set of properly set up coils, and just like Henry designed it, it ran great on battery, and even better when I switched it over to the mag! So, I would think you should make sure your coils are properly adjusted as the first thing you do. Good luck.
If you have a good mag, the car will run better on mag than on battery. The coils should be adjusted to fire at 1.3 amps. That will work on both battery and magneto. If it doesn't run very well on mag, it is usually a problem in the magneto, because the battery is 6 volts and the magneto is more than 6 volts if it is any good.
If your car runs significantly better on a 6-volt battery than on coils, it's time to phone The Coil Doctor.
Now, it may not be that your coils are the problem; it might be something like weak magnets or the wrong clearance in your magneto, but that kind of maintenance requires a knack (and it might be especially difficult to find a local mechanic who could do the job for you if you don't happen to have the knack), so I'd do the easy thing first and phone The Coil Doctor, discuss your symptoms with him and take his advice as to whether you need to send your coils to him for adjustment.
Oh, and I'd be remiss if I didn't also mention "Ron the Coil Man." He also does this kind of specialized work.
407 Stonegate Drive
Nicholasville, KY 40356
Phone 859 881-1677
I ran my '27 Roadster with a 12v battery. It came that way and ran real good. I finally recharged the mag and now after starting on 12v, I switch to mag and the RPM will come up a little. It runs good on either. PK
My mag has been dead for two years, I wired it so when I switch to mag it really switches to a 12 volt battery I have hid in the back this works great runs very well on 12 volts
I thought my mag was not working too well until I adjusted my coils using a Strobospark tester borrowed from a friend. Now it starts on mag with a quarter turn of the crank handle every time.
If you just want a cool looking car to drive, a T will run pretty well on 12 volts. 6 volts? Not so much. At least not at higher rpms. Acts just like the spark is retarded....and that is, effectively, what is going on.
However, if you want to EXPERIENCE the Model T, there is no substitute for the magneto. Some don't get it. They think that people who tout magnetos are a type of religious zealot called "Purists". For those who DO get it, there are few things more satisfying.
Hal, you be da man!KGB