My '14 T was running fine on mag until we switched out coils from another running car. After the switch the car would not run on mag but still ran well on battery. We checked out the switch on the coil box and the contact on the mag post, both of which were OK. After checking out everything else we could think of we finally put the old coils back one at a time with the car running on battery and switched over to mag. To our surprise, the car once again ran fine on mag and continues to do so after many starts and stops. I might add that the coils we switched out initially came from a car that was running well on mag with those coils. I have owned many model T's over more than 30 years and have never encountered anything like this before. I'm searching for an answer and hope that someone else has experienced this problem and figured out the cause, I'm stumped.
Val, you will have to provide more information on the coils and measure the Mag voltage on both vehicles for a likely cause or cure to be expllaned.
Are the coils the black plastic case type or new enough to have KW and a date stamped on one side?
Are the coils new enough to have small strips of metal for the magnet bar or do they have a small wire bundle for the magnet bar?
Has the coil box wood been painted with a shiny black paint?
Did you measure the Magneto voltage on both vehicles and was it about the same value?
One of the coils from each of the cars is black plastic and the others are all old Ford coils with the wire bundle. The coil box wood has never been painted. I will measure the voltage on my car tomorrow but don't have access to the other car any longer. I do have 4 coils somehwere that were rebuilt by Ron Paterson some time ago and plan to try them out on the '14 tomorrow to see what happens.
I had the same , the problem was a bad capacitor
I encountered this, and I think I figured it out.
I was doing my own research - later published in Vintage Ford - and I rebuilt a set of coils for a friend. His car was running OK on coils that had not been touched in living memory. So I expected good things when he fitted the new rebuilt set which checked out on an HCCT. Instead, it was much worse on magneto, though OK on battery.
I looked at his old coils and found that the cushion springs were not set up correctly - they didn't follow the lower contact down.
When they are set up correctly, the cushion spring pushes the upper contact down as the lower contact is pulled down by the magnet. Contact is broken cleanly when the upper contact is stopped by the rivet head. This means that the coil continues to charge up while the contacts move down. You get a bigger charge in the coil, and hence a bigger spark. But the magneto has to be able to provide a voltage pulse of sufficient strength and duration to make this sequence happen. A 12v battery will also make it work.
But if the magneto is weak, the points hardly move, the contacts don't open and there's no spark. However, if you have a cushion spring which doesn't push the upper contact down, the contacts open as soon as there is just a small magnetic force. You do get a spark - but not a big one, and probably not a well-timed one. But it will work with a weaker magneto.
When we re-magnetised my friend's magneto (in the car, with three 12v batteries), it all came right. I was much relieved - and so was he.
Thanks to you all and especially to Chris who I think has hit the nail on he head. My magneto is a bit weak and I seem to recall having to play with the cushion spring on a couple of my coils to make them work correctly. I plan to zap the mag and see if I get better results.
I would suspect that the voltage is different between the two magnetos. However before doing anything to the magneto, check both sets of coils on a hand crank coil tester and set for 1.3 amps. Check for a single spark at each of the points around the tester. Then try the coils again. If they run good with magneto, you have solved your problem. If not, your problem is likely the magneto, and you can check for voltage at the magneto.
This is what I think is happening. The car which won't run on Mag has less magneto output, and perhaps the coils which you substituted were set at a higher current and so they would not work on the car with the weaker magneto.
If I am right, your car will run a while longer with the coils set correctly, and eventually will need the magnets re-charged.
Val and Chris, a good catch here. I left out the most important question: Were the coil points replaced with recently new ones? That little flapper on the bottom of the brass top piece is the most important part and if it don't drop down that .005 inch, your coil will not function properly.
How can the cushion springs be set incorrectly (or not operating at all) and the coils check out OK on an HCCT tester?
That can only happen in the hands of someone who does not know how to properly use a HCCT.
Ron the Coilman
Exactly. And I assume there would be more than 1 spark at each point indicating an incorrectly set coil.
Three of the coils in the car that would not run with the other coils were clearly rebuilt by someone a long time ago and probably have not been touched since. The tops of the wooden coils are painted flat black which I know is something that Ron does as he has done many coils for me in the past but since I did not have them rebuilt I really do not know who rebuilt them, how long ago it was done or what they did. The only other thing I can add is that the car we swapped coils with is a fresh rebuild with a really hot mag. Putting it all together, based on everyone's input it sounds to me like it's a combination of weak mag and coil adjustment issues. I had Ron rebuild 4 coils for me a year or two ago and I carry one of them as a spare in each of my other cars so as soon as I can retrieve them I will try them in my car. If the car won't run on them it's a pretty sure bet that the problem is a weak mag
If you suspect a weak magneto I suggest you contact me directly so we can conduct definitive tests to determine your magneto's health.
That way we can tell if properly adjusted coils will work correctly.
Ron the Coilman