Gentleman, I humbly ask for a quick bit of advise as to where to look first to solve this issue. I recently installed a rewound coil ring. I did not check the gap (my bad) as I assumed should have been the same from when I took it out to when I put it back in. That being said, the car runs beautifully on battery low and high idle. When I switch to Mag, it continues to run smooth on low idle. NO trouble at all. But, it runs rough on high idle. I can drive the car on Mag, but it just runs really rough on high. I used an older mag post when I reassembled it. I figured there isn't much to a post other than just transfering the current. But, could this be the simple solution? Or is it a deeper problem. My confusion is how well it runs on low idle, but turns rough when revved up. Thanks in advance for any help.
I assume it didn't run on magneto before you replaced the magneto. Have the coils been properly adjusted on a hand crank coil tester or a Strobo-Spark? Properly adjusted coils may not run well on battery but run great on magneto. Your coils may be double sparking or not firing properly at the higher magneto voltage, but run OK on battery.. If that is the case, perhaps someone with a properly adjusted set could loan them to you to see if they work well.
Folks with a lot more experience will likely chime in here.
All 4 coils just came back from the expert Ron the Coilman. I am guessing they are ok. I have several others from him that I could replace just to make sure.
I was going to say multiple sparking, but if Ron has set them, it won't be that.
Perhaps carbon tracking in the coil box becoming evident because of the higher voltage would be next on the list.
(Message edited by 26tourer on March 18, 2015)
I think John H has the right idea. That's what I'd check next.
Have you checked the output from the magneto?
First check output from magneto. Then if low check for lint at the output plug. If no lint and output is low, try an in engine recharge. If none of the above work, pull the engine and set up the gap correctly.
If the output is good, the problem is very likely the coils are out of adjustment.
In the first place, why would you replace the ring if the magneto was working? I would if it was old and had brittle insulation. Not all magneto rings are identical. And the gap should always be checked whenever working on the magneto or even when working on the engine or transmission. A common problem is the thrust on the rear main bearing of the engine wears and changes the gap.
If idles good and runs bad at speed, how about changing your spark lever position and adjusting your carb.
Thanks guys. To answer a few of your questions and comments. This car was not running when I got it. I pulled the engine, honed the cylinders and replaced new pistons and rings. Unstuck and lapped and reset all of the valves to the correct settings. New gaskets etc. and found that a lot of the insulation was worn off of the windings and were exposed on the mag. So I had it rewound while it was out. Installed all new wiring. Used an old coil box, but new contacts. Like I said before, my confusion is while running on Battery there are no issues whatsoever. (I do need to have Ron rebuild my Generator. So, at the moment that is not hooked up.) But once I switch to Mag, the higher engine speed makes it sputter. I thought of the carb adjustment, but if it runs fine on Battery, then it should run the same on Mag. Right? And if the gap is not right, can it run fine on low idle and not on high? Purrs like a kitten with spark lever all the way down and throttle on low idle on Mag. Give it gas and it sputters. If it was a carb issue, wouldn't it act the same on both Bat and Mag? And last I don't know how to check the output, or what guage to use. Sorry! Still learning. Thanks again.
Thoroughly clean and relube your timer. Make sure it's in good shape.
I would think from your description that the problem is in the coil adjustment. Here's why. With the battery, there is a continuous sparking as long as the timer segment is in contact. If some of these sparks are weak or mission, you will still get enough spark to burn the fuel. With mag, the spark comes as the voltage wave increases. If that particular spark is missed, the car will misfire. A good check for this would be if you have a friend who has a T which runs good on mag, borrow his coils and try them in your car. If this fixes your problem, you need to adjust or rebuild your coils. By doing it this way, you would save the cost of rebuilding them if the problem is elsewhere. I looked at your profile and notice you have 3 T's. If any of the others run good on mag, try swapping coils. See if the coils you suspect run OK in your other car.
The reason I think your mag is working is that usually the sign of a weak mag would be the engine runs smooth at speed but won't idle on mag.
Anyway, worth a try. If you lived closer I'd loan you mine.
"Purrs like a kitten with spark lever all the way down and throttle on low idle on Mag. Give it gas and it sputters."
Have you tried retarding the spark when you try to run it at speed? You may have it too far advanced.
The sweet spot on my cars is quite different for running on Mag or battery and the difference is most pronounced at speed. Before I did anything else I would play with the spark adjustment and see if that does not clear up the problem.
Get a fb mag out put meter, it will tell you what is coming from the mag
Timer will really make one act up above idle, you didn't say what timer you are using. The roller timers tend to wear ridges and will cause the roller to hop at speed. The Anderson is touchy if not perfectly centered in the timing cover. Will most likely be something very simple, don't overthink the problem, good luck. KGB
I am new to Model T's, and have a mag that has a few spots that the insulation is scratched off . What can happen if I don't re insulate the coils? Can I clean , and paint on a rubber insulation?
Also, could the problem Charles is having be that the magnets are loosing charge, or one is in the wrong way?
You must have the engine and transmission removed. If so, and you want to use the magneto, I would recommend you buy a rewound one from one of the parts vendors. If not, buy the book from the club "electrical system" which describes step by step how to rewind your own magneto. I have rewound two using that method and both serve me well. The problem with cleaning up an old magneto with bad insulation is that you won't know whether it is useable until you get the engine installed. The labor saved if the coils don't work is well worth what it costs to replace.
Thanks guys, this is a great start. I will check it out when I get a chance. Hopefully this weekend.
Your coils are fresh rebuild by Ron, They will be ok, if not sure try them on one of your other cars.
Did you test the output of your magneto??
If not just take a 21W 12V light bulb and connect it between the magneto and the engine ground(-). Connect an ac volt meter over the lamp. Start your engine and make it run on battery. At idle you should read about 9 acV lamp should be yellow, at a brisk idle it should go to about 22 acV and the bulb should be bright, at full speed you should read 30+ acV and the bulb will burn out.
To do this test just disconnect the magneto from the car electric.
If the reading are low your engine will run as crab on the magneto and smooth on the battery.
Hope this helps
I had the same problem, but found a worn Timer Rotor was the real problem, probably my old Mag coil ring was good, as well.