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, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Q: I have a 1966 Honda CL77 305. We all know the charging system setup wasn’t the best on these 12-volt bikes. From the factory they were weak at best. I’m trying to figure out why the stator isn’t producing 60 volts to the rectifier? I have installed two different stators and replaced the rotor as well. I also installed a new rectifier and new coils. The bike now starts with one kick, but when I turn the lights on, I start losing the DC current, as shown using my voltmeter. I have checked the red wire, the brown wire and the yellow wire going to the rectifier, as shown in the manual. I have also replaced the headlight switch, and I’ve added a new wiring harness, too. I have also installed the electronic ignition from Charlie’s Place. The new battery is simply not getting up to 14 volts when lights come on. Lights on or off, the battery is losing voltage. I could go insane over this. — Bruce A. Ferguson/via email
A: We’ve been fighting a losing battle with these marginal charging bikes ever since full-time headlight use became law. It used to be that the bike would mostly be used during the day, long enough to barely get the battery to full charge. Then if you had some night riding, it would drain the battery, but hopefully not so much that you couldn’t make up the deficit the next day. I’m not sure those machines ever managed to charge a battery to 13 volts, much less 14 volts. I think your best bet is a battery tender, since you’ve replaced all the components with no improvement. MC