Posted by Bob on July 25, 2011 at 08:22:37 from (64.255.159.192):
In Reply to: Coil talk. posted by 641Dave on July 25, 2011 at 08:04:16:
The resistor adds resistance to the primary circuit limiting current to a safe value for the coil and points. (Typically 3 to 4 Amps, ignition "ON", points CLOSED, engine stopped.)
"True" 12 Volt coils marked "no external resistor required" have enough INTERNAL resistance (typically about 3.5 Ohms) so NO external; resistor is needed. (Example NAPA part # IC14SB.)
12 Volt coils marked "Use WITH external resistor" are more or less the same as 6 Volt coils (with a primary resistance of 1.5 to 2 Ohms), and therefore need an external primary resistor of about 2 Ohms.
(NOTE... there is some variation in coil primary and ballast resistor values, these or round figures.)
BTW, I'll bet you find your "spark problem" in the fuel system.
Oh, yeah, also check that the distributor's speed advance is not stuck and is operating properly.
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