Running issues

[Dennis Pings]

I have a 1922 touring and lately I have had an issue with it running on magneto. I start it and warm it up and switch to magneto. It runs well for about 20-30 minutes. Then it starts spitting, sputtering and backfiring and then it will shut down.

When it will run on magneto, I have checked the magneto with a lightbulb and increased the RPMS and it gets really bright. I know it's not a fuel issue because when it starts to act up, I can switch to battery and it runs just fine. I have pulled the magneto lead and there isn't lint on it from the bands. I would think if it was a coil, it would act up but would continue to run.

I'm hoping someone here has an answer of which direct to go.

[DanTreace]

Could be switch related, if internal contacts wander off, that would simulate the issue. Keep heavy key chain items off, they sometimes can sway and wiggle switch key.

[Norman Kling]

Does it change with the speed of the engine or the position of the spark lever? There is a difference between the way the timer works on magneto than on battery. On battery the current begins to flow when the rotor first makes contact with the segments in the cap and remains the same until the rotor passes that segment. However on magneto, the AC voltatge starts low and peaks with a sine wave. If one or more of the coils is out of adjustment, that peak might be different with each coil and the spark will come at a different time. You will probably notice that on battery, the timing changes with the movement of the lever. However on magneto, your timing comes in what I call "nodes". It will stay about the same as you move the spark lever until suddenly it either advances or retards according to which way the lever is moved. If the coils are out of adjustment, the fine timing could vary from coil to coil with the lever in the same position. Another thing which could cause it to run rough would be needle valve adjustment in carburetor. but that shouldn't make much difference when on battery or magneto. And of course the condition of the electrical connection from the magneto plug through the wiring to the switch and finally to the coils. So check all these things out. Whatever you do, be SURE not to accidentally connect the battery to the magneto or you will ruin the magneto.
Norm

[TRDxB2]

Could be switch related, if internal contacts wander off, that would simulate the issue. Keep heavy key chain items off, they sometimes can sway and wiggle switch key.

I lean towards this as well. When the key is turned to either MAG or BAT one should feel the contacts settling to the indents that are on the backing plate.

[TWrenn]

Could be switch related, if internal contacts wander off, that would simulate the issue. Keep heavy key chain items off, they sometimes can sway and wiggle switch key.

I vote for the switch also.
Try it on battery for a day and compare.
I have the exact same issue with my '26 Fordor. Winter project...work on switches. Yes plural...I also have a repro that is even worse!

[speedytinc]

If its the internal switch contacts, jiggling the key would effect a change running when on mag.
Try that experiment.
Weak & dirty internal contacts can be cleaned & bent for more contact pressure.
This is a common issue.