It's me again. I've posted so much about coils recently that it made some people's head spin. This is not altogether about coils but forgive me if I mention the c word. I/we drove our '21 Touring for the first time Saturday, two weeks ago. It seemed to run fine until the evening when I changed from Bat to Mag at about half throttle, causing it to backfire and blow up the muffler. The following Saturday, with the repaired muffler in place, when we tried to drive it , it ran poorly. Since then I have put in a set of c---s borrowed out of a running car. I also took off the new timer and replaced it with another new original type timer. It runs better now but still has a skip from time to time. Tomorrow I will disassemble and clean the newly rebuilt carburetor.
First, you will want to swap from battery to magneto at a low RPM and minimize the time "off" to minimize the charge of raw gas that makes it to the muffler. Right after starting is a good time to do it.
Second, based on your previous questions and quests, I'm going to guess that no coil ever put in that car has been both rebuilt and properly tuned. Coils that have been will have the car pick up in speed and performance when switching from 6VDC to magneto. Coils that are adjusted to any old setting may run better on battery than mag or only run on battery or only run on mag. This is the benefit of setting the coils with service equipment meant for the job.
That said, there is a possibility that a piece of lint from a band, or other trash has gotten tangled up in your magneto post which will cause the car to run erratically on magneto, or sometimes, not at all. You may want to pull the mag post off the top of the hog's head and inspect for something like that.
Good luck, and know that pretty much every T owner that ever lived has blown up their muffler, myself included.
Tommy, Clean and gap the plugs. When I have the issue you describe it is usually caused by fouled plugs. Plugs will foul if you start it and run it without getting up to operating temp. I see this problem if I start the RPU and back it out of the garage several times without really driving it any distance.
Thanks Scott. Yes I learned that lesson my first day driving a T.
I'm pretty sure the borrowed coils have been tested, on a machine, if not rebuilt. And now my car runs better on Bat than Mag. That first day it seemed to run better on Mag, which was a good thing as I have not got my generator working yet. I will clean the Mag post tomorrow as well. I hat to admit it, because it means my car is no longer original, but last time I had the Mag post out I replace the screws with socket head/allen screws because one is tough to get to. Don't tell anyone, ok? I have two new Champion plugs like the ones in my car that I can swap in tomorrow as well.
Do a search on the John Ragan magneto test. You'll need an 1156 bulb and an analog volt meter. Don't substitute the bulb or try to use a digital meter. Test the mag and determine if it is weak. Might need a magnet recharge. How's the crankshaft end play?
Is there a chance the repaired muffler wasn't assembled correctly?????