Magneto Problem

[Jugster]

Since I bought my Model T a dozen years ago, my engine has always idled faster on battery than on magneto. I have always suspected that my magneto's output might be a little bit weak, but that condition has gotten more noticeable lately.

Today I was driving the car and it was running just fine. Then suddenly, the engine backfired and quit. I was able to re-start easily on battery, but the engine wouldn't run on magneto. Perhaps my magnets need recharging? Or perhaps it's something else that I'm overlooking? Are there adjustments that can be made to the magneto from outside the engine? Could it be a problem with the connection at the top of the hogshead? Any ideas out there?

[Rich P. Bingham]

First thing to check would be the mag post on the hogshead. Not infrequently band lint or other stuff circulating on the oil will either short it out or interfere with the connection.

Magnets can be re-charged in the car, a weak mag often indicates an improper gap between the magnet clamps and the coil ring cores. Sometimes this can be corrected with a newly re-babbitted crankshaft rear main cap.

Good luck ! Let us know what you find !

[speedytinc]

Your description is of a weakening magneto. How much fore & aft crank movement is there? As the gap widens the output weakens. This doesnt explain the sudden non function.
I would attempt an in car magnet recharge with a DC arc welder.

The sudden non function is a common symptom of a bit of band fuzz interfering with the mag post connection. Or a possible introduction of battery voltage, possibly from a bad ignition switch.
Check/confirm a lack of output with an analog AC voltmeter.
Pull the mag post & clean the spring/spike. Then test for output with an analog AC voltmeter.

[Steve Jelf]

Easiest stuff first. Check all connections carrying current from the mag. That includes the switch. Sometimes a loose wire or a poor contact in a switch can be the problem. You very well may be due for a magnet charge, but I doubt that running weakly then suddenly not at all is due to weak magnets.

[TXGOAT2]

Is your spark control linkage working right?