MTFCA Forum

I have a 1921 touring. Two years ago I had the engine rebuilt and it has been running like a trooper up to 2 weeks ago.
I have been on 3 tours and the last one was in Lexington Michigan. That's when she developed a miss.

I nursed her home and then started to look for the problem. Gas was getting through nice and clean. Spark plugs were cleaned and gapped.
No change. The roller timer was a little rough so that was replaced with new. Still missing and at this point the #1 plug was not firing.
Replaced the #1 coil. Now it won't fire and is back firing.

So I checked all the connections and placed the spark plugs on the block. Turning the engine by the crank I got spark on #1,2,4,3 in that order.
When the #1 is sparking the piston seems to be at the top. Reinstalled plugs and it still will not start and is backfiring. When the plugs are removed they are wet so to me that indicates they are getting gas.

What am i missing?? Any suggestions would be appreciated.

Does it do it when running on magneto, battery, or both?

Did your car get rained on, either running or parked, or did you wash it? A damp coil box or any other part of the high tension side of the ignition system can cause issues. If you have wooden parts in your ignition system, problems may persist even after everything is completely dry.

Mine doesn't run on mag. Battery only the last years.
Did have a bit of rain on tour but coil box was dry and in good shape.

Do a compression test. All cylinders should be about the same compression. Also check for an intake manifold leak. if it is drawing in air, on one side of the manifold, it would cause a lean mixture. This could cause a backfire. Especially if it spits through the carburetor.
Norm

Great suggestions!
Tomorrow at the shop I will check the box and connections again and do a compression test.

Don’t do any tare down removing engine parts or whatever.
Ck all the electrical connections, timer wires rubbing on the block, especially the coil box, wiring, any area where it could be grounded.
IF YOU ARE IN A GARAGE START WHEN ITS DARK OR AT NIGHT. Check the car and see if there is any sparking or any connection not arcing when a wire is taken off and on. A loose nut on the coil box can give you fits. Been there and done that and that’s all it was on my car. I should have checked it first but didn’t.
Good luck!