QuestionI just cannot find a factory spec for primary resistance for a 1968 CD175 coil. It's a single coil that fires both plugs, 360 degree engine, 6V with points of course.
While quite possibly irrelevant, I did find a factory spec, in the Honda dealer service manual that I have for a 1981 Passport C70, It is also a points ignition, 6V....and the spec for primary resistance is 1.35 -1 .65 ohms which surprised me.
I measured some other 6V honda coils of unknown provenance and got in the 1.4-1.6 ohms range....
Thanks one million percent! I bought your 250/305 guide maybe 20 years ago and still refer to it often!
Eli
AnswerEli, the coil resistance figures are usually pretty consistent for any type of points type coil. The 250-305 12v coils are usually about 4.5 ohms. Theoretically, a 6v coil would have about half that resistance value, making them read out around 2 to 2.2 ohms, but I can see how they could dip down into the 1.6 range on a single cylinder model, as you have discovered. If it makes sparks, doesn't overheat and doesn't melt down the points, then the coil must be about right for your bike.
Coils are still subject to ohm's law and you don't want the current across the ignition points to be more than a couple of amps.
I'm glad you have made good use of my 250-305 guide!
Bill Silver
