Intermittent Charging on a Yamaha XS750
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Q: I have had an intermittent charging problem with my 1978 Yamaha XS750 Triple since the day I bought it. I bought it two years ago with 18,000 miles on it, and now it has 20,000. The previous owner installed a new regulator, so the first thing I did was install a new battery and repair the wire connections at the stator (it had been dropped and it pinched one of the wires). I use an amp meter on the battery side. When charging, it shows 5 amps at 2,000rpm with the lights on, which I think is a bit low, but according to the Yamaha manual I have is what it should be. But I find when I ride it the charging becomes intermittent and eventually drains the battery. As an experiment, I took it on a 75-mile round trip, with a friend in front of me, for safety reasons, and one following. It may be coincidental, but it seemed when I would hit a bump in the road it would sometimes alter the charging state. I have checked and rechecked all the connections and repaired a few of them to no avail. Would the headlight perhaps cause this, or do you have any suggestions?
— Dennis/via email
A: I think you found the obvious fault in the pinched wire, but perhaps there is some hidden damage in the stator windings that shorts out when jarred. You could try a used alternator from eBay, or go whole hog and get a rebuilt one from Rick’s Motorsport Electrics. The latter is more expensive, but you know you’ll get a good unit. If you’ve checked all the visible connections, that leaves the ones you can’t see on the inside of the case.
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