I just finished reading the November 2008 issue of Farm Collector. Regarding the letter "Another theory on the Farmall kick":
With all due respect to the different opinions concerning magnetos, starting with the impulse: The impulse performs at least two very important functions. When the latch engages it stops the magneto from turning, yet the drive shaft is still turning and winding a strong spring. This retards the spark the correct number of degrees, 35 on a Farmall. This prevents the engine from kicking or firing too soon, or before top dead center.
When the latch releases, the tightly wound spring gives the armature a quick twist, which produces a very hot spark at top dead center. After the impulse is released, the spark will fire 35 degrees before top dead center. The E4A and F4 mags have 35-degree lag angles on the impulse, which also means 35 degrees of advance after the latch releases.
The E4A mag definitely has a condenser. It is hard to see because it and the coil are both located in the armature!
The breaker assembly also turns with the armature and operates off an internal cam in the magneto frame.
A very important fact about magnetos is that different engines and different magnetos quite often have different degrees of lag angle and advance on the impulse. Lots of times most any old mag can be made to mount on the engine.
Example: If you mount a 25 degree mag on a Farmall, which requires a 35 degree mag, when you time it so it doesn't kick when you try to start it, you find that you are 10 degrees late on the timing when the engine is up to speed. There is no practical way to correct this except to install a 35-degree mag on a 35-degree engine.
Most E4A IH mags had a manually engaged impulse. A few of the later models could be had with a BX of BH automatic impulse similar to the F4 impulse.
A lot of Farmall Regulars, 10-20s, 15-30s, etc., were converted to F4 IH mags with automatic impulse in later years. It was more convenient, plus the F4 is definitely easier to work on than the old E4A.
My greatest respect and best wishes to everyone. I most sincerely hope that I have not offended anyone. These are my opinions based on 60 years of experience working on old machinery and thousands of hours of research and study of my favorite pastime of trading ideas and information with my friends and neighbors.
If you come by this part of the country in your travels, stop in a sit a spell. The coffee pot is always on. There are no strangers in this life - just friends we haven't met yet.
Don Price, 716 19th Ave. N., Clinton, IA 52732