Need Help With Automotive Coil

[FJmonkey]

As the unofficial First Post moderator for the club I also concur, now give us a proper introduction..... Tell us about your self and the bikes you have and have had.....Pets, children, Potato Cannon???

[Arnie]

You've just described the system common to many English cars and bikes that I know was used into the 70's at least. 
My '71 Norton Commando (in pic) had no starter motor (other than my leg) and had this system with 6V coils and ballast resistor in an otherwise 12V system.  It was hard to start.
The fix for that was to remove the Luke'sAss 6V coils and throw them in the darkest corner of the shed, replacing them with K-Mart 12V coils intended for Chevy V8's.  Now you got a hot spark, good to over 7,000 rpm (redline), and easy starting (sorta).  You did have to modify the ignition cam to reduce the dwell or you'd flatten the battery.

Cheers,
Arnie

I know that your problem is solved now, but just something to remember for next time. On really old cars, starter motors were not as efficient as todays models - they would consume high current and often cause a volt drop in the battery of around 2 volts at the time of cranking. Consequently acoil designed to fire on 12volts would produce very weak spark at the time that the engine was being cranked often resulting in a no show from the engine. As a result coils designed to fire on 9 or 10 volts were installed and the wiring was done in such a way that when the ignition key was set to the start position it would feed current to the coil directly from the battery but when the key was set in the run position it would feed current from the battery through a ballast resistor first ( to drop the voltage by around 2 volts) and then onto the coil. Now taking this theory into account is there perhaps just a small possibility that the parts store was supplying you with 12 volt coils all along. This could readily account for why you were getting weak or no spark, because at the time of cranking, the coil was only being fed with around 10 volts (even with a strong battery)

[Duane.Hoffeldt]

Thanks for the positive feedback lads. As a newbie you kinda feel anxious that your first post will get acceptance from all the senior contributors. I will drop an introductory note about myself shortly.