Dim headlight on idle

[section8joe]

On m newly purchased bike my headlights go dim at idle.
I just put in a new battery. I'm thinking it's the alternator. I'm thinking that the bike had the alternator replaced already since the colors don't match up and the electrical harness. Can it be the rectifier/regulator too? By the way it's an 83 heritage special.

 

[jamesgs4]

They all do that, the bike isn't charging at idle.

 

[MB-Ian]

Mine does that.. in fact so does my car (its not a modern car).

As I understand it, even if the charging system on the XS650 is working well, the engine wants to be doing 2500-3000rpm to be properly charging the battery = bear this in mind when doing lots of slow speed/low rev riding.

I.

 

[xjwmx]

Yep, in fact goosing the throttle at idle and watching for your light to get brighter is a common way of checking that your charging system didn't fall off a mile back.

 

[gggGary]

That's why Yamaha calls for a 1200 RPM idle, to keep the battery from going flat.

 

[XSLeo]

On my 75 with the Chrysler/ Radio Shack mods for the reg/rec With the headlight on and a few minutes to recover from using the electric leg. Reving the engine to 1800 rpm brings my volt gauge on my handle bars up to 14.5 volts. So on your 83 with the solid state reg/rec should be close.
Hook a volt meter up and check your charging system. At idle about 12 volts with the lights on is about right, now rev it up slowly. As the revs increase watch the voltage. It should climb up to 14.5 volts by about 25-3000 rpms. If your battery is good and everything else is working good it may reach 14.5 volts sooner.
As you cotinue to rev the engine it shouldn't rise above the 14.5 volts. All this voltages are + or - .5 volts.
If your bike passes this test then be happy.
Hooking a volt gauge to your bike is a good idea. You can find them at most any parts store, Wal Mart. I got one from Harbor Frieght. Hook one lead to ground, the other lead to the main circuit brown wire. In the headlight bucket you can find both.
This way you can moniter the voltage at all times. If it starts to read low at any time, you need to trouble shoot your charging system soon.

 

[pyrocentric]

Yeah, my bike breaks even at about 1300rpm. You have to go above that to start charging. It took a lot of connection cleaning and troubleshooting to get to this point, so I'm happy.