MTFCA Forum

My '27 will start on battery but runs rough. It idles smoothly on battery once started but misses when you rev it up. Adjusting the spark lever makes little or no difference. When I switch to mag it clears up and runs fine. The battery is good and cranks the starter over without any problem. Any suggestions?

If your battery is fully charged and in good condition, I'd check the spark plugs and timer. If those are good, you may need the coils adjusted.

An ignition switch problem is a possibility.

Have the coils tuned. Best guess is the amp draw is a bit high. The ignition system is happier running on the higher mag voltage. This is typical.
T's run poorly on 6V.

Thanks for the suggestions. I will switch out the coils from another one of my T's first and see if that doesn't clear it up. If not then I'll work on the timer.

Another thing to consider when running on battery is that once the engine is started, the timing will need to be advanced immediately, and usually quite a bit more than may be required when running on magneto at similar engine speeds.

Does it still miss occasionally after a warm up on battery? If it does try adjusting the carb slowly and then rev it up on battery. Other than that probably a coil issue. Even the best running cars will sometime miss a bit until a warm up. A regularly driven car will usually run the best than one thats an occasionally driver.
And as always T’s run best on Mag.

I think it is the adjustment of the coils. I drove one for about 5 years on 6V battery and it ran smooth but not as much power as on magneto. This happened because the funnel broke off the oil line and cut the mag coils. Fortunately I had a magneto plug oil line and no problems with the oil. Later I rewound a mag ring and fixed it. That was when I found out what had caused the magneto to fail.
If you are driving along and realize you didn't switch the key to mag, don't switch while moving. in gear. Put in neutral and idle the engine. Otherwise there is a chance you will blow the muffler.
Norm

Went to swap coils and found that that the coils from my '14 just won't fit in the '27 coil box. Don't understand why that would be as they are all Ford script or K&W coils. Even the coils I had in the '27 coil box are a very tight fit but I was able to get them out one at a time eventually. I found a few extra coils that I had which I could get in the box with no small amount of effort and that cleared up the problem I was having running on battery but I am still puzzled by the fact that the coils from my '14 would not fit. I always thought that Ford coils and K&W coils were interchangeable and were a standard size.

Coils that have been overheated may be slightly oversize or otherwise distorted. Coil boxes can vary, also. Some coils have prominent solder contact buttons, and some do not.

Don't like the way your car starts on battery? runs fine on mag, simple fix, follow Fords manual instructions on how to start engine and use magneto.

That's what I was doing after the problem started but I never had an issue before and I wanted to find the source of the problem and correct it. I rarely use the starter and usually crank start on battery but my back is not up to crank starting on mag so I wanted the problem resolved. Always started on battery before with the hand crank and ran well enough before I switched to mag.