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Regulator/rectifier going bad? Also no left turn signal.


CB750 Enthusiast
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Crawfordsville, IN
I put a fresh battery in my bike and after 3-4 weeks it wouldn't start. I charged it over night and there were no problems the next morning. When it gets low my headlight starts to flash a little, especially when using turn signals. Is the battery not charging?

About turn signals, my left one doesn't flash. I hear the tone for it, and sometimes it'll flash at 5K-7K RPM but not often.
Sounds like your not charging very well. Get yourself a multimeter, check the volts on your battery, volts should climb up to about 14.5 revving up to 3K+. If they don't climb, or don't climb that much (~12.1), you not charging or not enough. If you're going over 14.5, you are over charging and will wreck your battery. A new fully charged battery should be about 12.5 volts.

Turn signals start to act funky when the volts are low. The blinker/flasher units work on load. When there is a load, it will turn off, then back on. If the volts are low, then there's not enough for it to sense that it needs to turn off. Also, if there is some resistance, like a corroded connector, the flasher wont feel the load and not flash. For example, on the bike I'm working on right now, the Right flashes faster than the Left, so I know someplace on the left side I've got some resistance I have to clean up.
I would agree with Grepper. I thought my flasher was bad but happened to rev it up a little after cleaning the terminals. The blinkers suddenly started working. Got a new battery and they worked even at idle.
I haven't had the chance to look into this at the moment, mainly because I can't keep my bike idling to check everything. But I'll update it when I find out more.
Got a replacement regulator/rectifier circuit from cb750supply and swapped it out. Everything seems to be working alright as far as the battery charging. I bought a new battery a few months ago when I got the regulator and haven't had to put the charger on yet. As for the turn signal I think I have a loose wire somewhere, sometimes it works, sometimes not.

I am still in school for a year, maybe two, then I can get a good job, a newer bike and get real engineering experience from this bike.