I have a 1925 T model but my question is for my1911 Carter car. I have a DU 4 magneto and I have sent it out for repair 2 times. When it comes back I put it on and the car starts. The next day it will not fire. What am I doing wrong? Thank you.
Maybe the magnets are being discharged. Is there a chance a battery current is being introduced to the system and discharging the magnets?
I've read too much spark plug gap will burn out the armature of a magneto, but I would that would take some running time.
Did the rebuilder list what the repair(s) were? That may help you determine what is happening.
Is it rotating the proper direction? There are both clock and counter-clock wise rotation DU-4's. DU-4's are pretty bullet proof.
What are you using for the control switch?
Is your DU-4 a dual or duplex or an independent?
I have a similar problem with a DU4, but it takes 6 months before the magnets become weak.
If you turn it by hand on the bench out of the engine, will it give sparks ?
Did the repairer test the magneto with a device at the same speed as it will turn on your engine ?
It looks like there is an internal short-circuit coming only after the mag has run.