My 25 Tudor has started to misfire on mag. runs perfect on 6 volt. Coils perfect, cleaned mag post pickup and checked all wires. This started while driving on mag when the engine died. Switched to batt and then back to mag and worked fine until I ran it again. Checked mag output with the bulb and volt meter. The light gets bright but flickers some. will not get bright enough to burn out and only shows about 14 volt. It will start on mag with just a slow pull of the crank. Is it time for a magnet recharge?
Try a different mag post.That one may have an intermittent short.
Fourteen volts is kind of low,but the fact it still starts on mag leads me to think mag post.Early repops were not all good.
Check your switch--if it starts on mag with a slow pull on the crank, I wouldn't suspect a weak mag.
Do check for debris on the magneto post contact. Lots of times gunk mixed with tiny metal particles in the oil if stuck at the contact can cause a intermittent or permanent ground.
Oh, didn't carefully read your post Jim, you did that!
I'm much more suspicious of the switch. This sounds typical of problems there.
Don't know without looking at it but the mag post could be your culprit. I installed a newly rebuilt Mag ring in my 1919 Runabout and after driving it for a while it stopped running on mag. Upon inspection with a mirrow to look down in the hole for the post I found that the top button on the rebuilt mag ring was just off center enough not to make a really good contact. I bent the mag post spring over to one side and it seems to have solved the problem. It quit on mag twice before I discovered this. Don't know if this is unusual but it was my problem.
Don't overlook a dirty timer. Esp if you are running one with a carbon brush. Your situation sounds real familiar to me.
It could well be the switch.BUT,the flickering of the bulb makes me suspect mag post.
Even at idle,the mag cycles so fast you could not see a flicker of the bulb.
Also,l suppose on of the coils on the mag ring may be shorting out.You may be able to burn that off with an in-car recharge,if that is the case.
You can stretch the spring on the mag post. The later ones are easier to stretch. When installing the mag post, you should have to force it down somewhat while tightening it. If you have an early mag post, I've turned down the warped tops of them a bit, and even though not authentic on an early one, I like the mag post retainers used on late models.
When you measured 14 volts did you use a digital volt meter? I also would ask if you had the 1156 bulb in a loose fitting socket since that could trick you when watching the bulb flicker. Some of the mag posts have an oil line out the side and I have seen some where the threaded fitting into the mag post for that oil line is in fact threaded in too far and shorting against the center electrode and causing the mag to not function. Eliminate all sources before you attempt to recharge your magneto in the car since that should only be attempted when you have nothing to lose. Sometimes a magneto gets weaker if the recharge is not done correctly.