For proper operation, the impulse coupling must work properly. The impulse coupling is the device that you should hear clicking or snapping when you crank the engine.
If the engine has been sitting in the sun or other hot environment for long periods, it is likely that the tar insulation used on the magneto coil has melted and run down onto the armature causing drag and preventing the coupling spring from releasing the energy stored within. This will prevent the magneto from developing proper starting voltage making the engine difficult or (more likely) impossible to start.
If you do hear the coupling clicking, inspect and clean the points. Use an IBM card or piece of brown paper bag to clean the contact points. Do not use a point file.
Note: Your FM magneto has a gear driven rotor beneath the outer bakelite cover. Remove the cover carefully and be certain to properly time the gear upon reassembly. The gears should have timing marks but I advise marking with paint, etc., in case you cannot see them.
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Today's Featured Article - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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