Coils are designed to operate with or without ballast
resistors. Coils that run without them are capable of
handling full battery voltage and the heat that this produces.
Coils that run with ballast resistors are designed to operate
at approx. half of battery voltage. During low speed operation
the points are closed longer, and the resistor heats up to
restrict current flow to the coil.
Less voltage is required to fire the plugs at low speed.
As engine speed increases, the points stay closed for a shorter
duration and the resistor cools off. This allows
more current to flow to the coil, for increased spark output.
Your Lucas coil runs ok because it does not need a
resistor. The others you tried probably require one to keep
the coil from overheating. I`ll shut up now and give someone
else a chance.
paul mcbride
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