Intermittent Charging on a Yamaha XS750


| 12/20/2017 12:00:00 AM


Tags: January/February 2018, Yamaha, Keith Fellenstein, Tech Corner,

Motorcycle Classics tech expert Keith Fellenstein

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 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

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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.

Clint
12/28/2017 10:06:51 AM

These are not a permanent magnet alternator so the connections from the fuse block to the alternator need to be in good condition as well. If he is still running the original fuse block it may be the issue. They have failed with no visible damage to the tabs. An intermittent break in the alternator would be very rare.





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