Electrically Handicapped Please Help, 1981 XS650 won't keep battery charged

[Bruce Wayne]

Aloha Everyone, hope your Friday afternoon is going well!

I am just beginning my weekend wrenching and for any and all who care to read or help out this is what I've got so far


1981 XS650 Stock ignition/charging system.

Here's what I know...

-Bike will start and run great, when the battery is charged up. I can get about 50 miles on a charged battery before the bike will shut off due to low voltage in the battery. When it dies, sometimes a lucky kick start can limp me home if I keep the RPM's high. But the solenoid will just click otherwise if I try to start it with the ignition.

-This has happened twice in the last 2 weeks.

-The Battery will take a charge/maintain charge. It is a couple years old though.

-I have run some of Curly's tests and here are there results...

1. Slap test works, wrench sucks right in when the ignition switch is turned on.
2. Headlight gets brighter as the engine revs.
3. I saw no voltage change when I shorted the green wire to ground and revved the engine. It stayed constant.
4. The brown wire connecting to the positive brush showed very similar to the voltage at the battery with the ignition switch on. The battery read at 9.56 , and the voltage at the brown wire was 8.86.

Known Problems So Far:
1. I found that the screw holding in the brown wire was super loose when I took the cover off. I could move it with my finger...


I will run some more tests tomorrow morning but I wanted to post on here to get some thoughts from any who are kind enough to help out. Thanks for your support!

 

[XSLeo]

Well, doing voltage tests with a dead battery won't help much.
On the voltage difference between the battery and brown wire should be about .2 or .3 volts. If more than that there is a bad connection somewhere between the battery and brown wire. Most often the key switch, they can be taken apart and cleaned. Fuses, round glass fuses sucked when the bike was new, All these years didn't improve them. Replace the stock fuse box with new fuse holders that use the blade type fuses. Follow the power along the red wire to the key switch and the brown wire coming out. You may find a dirty connection. They can be cleaned too.
The loose wire you found can be the culprit, maybe not. Have you pulled the brushes and measured them? Have you checked the rotor ohm's? Have you checked the stator ohms? All these tests can lead you to the problem.
Leo

 

[Bruce Wayne]

Thanks XSLeo,

The battery was at 12.5 fully charged when I put it on the bike today. It had been on a trickle charger for a night, then sat in my truck for a couple days. Today it read 12.5 when I started the tests. After starting the bike 4 or 5 times and letting it run for 10 minutes the battery is now sitting at 11.4. Which is alarming to me that it dropped that quick...

I packed up for today, but tomorrow I will check connections from the brown wire and see if I find anything.

My fuse box has been replaced, though I replaced them with inline fuses, still with the glass fuses. Tomorrow morning I am going to pull the brushes and also check the ohms on the rotor and stator.

 

[gggGary]

What voltage a re you getting while it's running? Hint you really want a voltmeter rigged up you can watch while you're riding both during at a least for a while after you think you have found the problem.

During testing move your leads around and compare, ground on engine, frame, battery terminal. +12 on brush iggy coil red out of iggy switch battery terminal. Check both idling and revved a bit.
Hint little cigarette lighter digital voltmeters are everywhere for <$10 guty and hard wire to the red inside the headlight shell or some other scheme.

 

[5twins]

Yes, you seem to be getting a wee bit ahead of yourself here. Do the simple charging test first. This will tell you whether it's really the charging system or just a bad battery. Clip a volt meter to the battery at rest (bike not running). Now start the bike and check at idle. Volts should rise slightly but may not if the headlight is on. In fact, it may read slightly lower. Now rev the bike up to between 3 and 3.5K. Volts should rise to around 14. If this checks out, the battery is most likely the culprit. If you get no increase in output then yes, you do have a charging system problem. Now you can start testing components to find the problem.