® In Defense of 70s and 80s Honda Charging Systems

The historic and beautiful CB750K0, with its 210 watt charging system, was seldom considered incapable electrically, until today.

The Internet will tell you that Honda's SOHC fours of the 1970s have troublesome charging systems. That the systems break even at 3,000 rpm (though this is false and they never describe the process of measuring breakeven so it is doubtful they know how) and you better not put a stronger headlight on or high performance ignition coils or your battery will go dead. They regularly warn their members to not install ignition coils having under 5 ohms resistance. They are adamant about this, like it's a scourge, an epidemic.

One of the things that keeps coming up is the fact that these systems don't charge at idle. This of course is correct. But this is not a defect. I know of no original-spec Honda electromagnet charging system that charges at idle. But they do start charging right off of idle, in most cases by 1300 rpm with the headlight off.

I suppose if you run the headlight on all the time, if you wear heated clothing, if you never get the tach over 4,000 rpm, and if you maintain your bike the many vintage Honda owners do--including embracing Wal-Mart batteries and Chinese electrical parts--then you could experience some issues. My two CB500 fours, my first one that I rode in the 70s and sold with 92,000 miles on, and my current one that I've ridden for eight years, both (had) have better headlights and 2.2 ohm ignition coils, and have never had any charging system issues. The forums discredit Honda's instruction in the official manual about adjusting the voltage regulator, treating it as some voodoo procedure that is harmful to your bike. It's not.

Don't forget that I offer a how-to book on troubleshooting the SOHC four charging system. It contains methodical instruction from a factory trained tech who really likes these old fours and was there back when these bikes were new, and worked on them every day in busy metro LA area authorized Honda dealerships. Known problem areas, factory issues, wiring repair, repairing the fuse box, testing the keyswitch, adjusting the regulator, and much more, including the best multimeter technique. You can find the booklet at this link. I think you'll find it comprehensive and resourceful.


Last update pd January 2025
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