You may have slightly excessive voltage drop from battery to the coil but it is not far off. This is the very exact reason that almost all manufacturers use a external ballast in ign circuit. They use that extra terminal on the starter solenoid or starter magnetic switch and run a wire that goes directly to the ign coil, bypassing the external ballast when cranking. Your normal cranking voltage at battery will be about 10.5 volts so you can see you will be getting only about 9.5 volts feeding your 12 volt coil while cranking. This lower voltage will then reduce the amperage flow through the coil and it is the amperage flowing that creates the magnetic field in coil, and when points open, field collapses and creates high voltage in secondary circuit of coil. Less magnetic field, lower secondary voltage available to fire plugs. The best way to , (if I was working on your tractor,)get a better starting machine in your case is, six volt coil , external ballast and different magnetic switch on starter that has the terminal for ignition bypass. That way you would be feeding about 9.5 volts or more to the coil during cranking. Good hot spark.
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Today's Featured Article - Two-Brush Generators - by Chris Pratt. Whether for product liability or because the aftermarket parts and labor business is lucrative, this concept is disturbingly prevalent. Fortunately when you step into your shop and make that jump 50 years back in time to work with your old tractor, this concept goes out the window. Even so, when it comes to the charging system, people quickly revert to this idea and start replacing the major components one at a time until it works. The reason you don't find any decals in your replacement set wit
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