Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject.
Commando electronic ignition
Q: I have a 1971 Norton 750 Commando Roadster and want to go to electronic ignition. Do you have any recommendations? I’ve been to numerous websites and looked at what they are doing at Colorado Norton Works and other places, like Australia. I want to leave the external looks pretty much unchanged so I want to keep the coils. Any help would be greatly appreciated. I really enjoy reading your column in Motorcycle Classics. — Barry Pittman/Topeka, Kansas
A: There are a variety of electronic ignitions to choose from. I’ve used two different brands and installed a third brand on a friend’s Commando. My 1974 Commando came with a Boyer, a decent enough ignition if a little old-fashioned. I changed it to a Power Arc optically triggered ignition I bought from Old Britts in Enumclaw, Wash., and I’ve been happy with it. If I don’t let the Norton sit for weeks between starting it, it will start on the first kick. I installed the Tri-Spark ignition on a friend’s Norton; it was the subject of the How-To article in the January/February 2012 Motorcycle Classics. His Norton is now also a reliable one-kick starter. The Tri-Spark and the Power Arc mount inside the stock points cavity of the engine, so there is no external indication that you have anything other than the stock points ignition. In both of these setups we opted to use a dual-output coil instead of the old Lucas coils, but you can use the Lucas coils with one change. Since all of these electronic ignitions are wasted spark, firing on the compression stroke for one cylinder as well as the exhaust stroke for the other, you wire the coils in series. In a 12 volt system, that requires using 6 volt coils so that the load on the battery and ignition is the same as if it were a discrete spark. Your current setup has two 6 volt coils in parallel along with a ballast resistor. You can keep the coils, but remove the ballast resistor and the points condensers. The ignition manufacturer’s instructions will spell this out in greater detail. I would recommend either the Tri-Spark or the Power Arc. They work well and with the right coils will keep your bike looking stock. MC