charging issue

I've got a new-to-me '78 650 SR.

New battery. With a full charge on the battery it turns over great. With a couple hours of riding, the battery loses juice. The bike runs fine if I kick start it, and the lights/signals work fine with the engine running. However as soon as the bike is off, the battery's worthless and I can't use the ignition and the lights are dim.

Is this an alternator issue? Why would the lights and signals work fine only with the engine running?

I'm a newbie here, so please take it easy with the big words. Thorough explanations really appreciated!

Thanks!

Post edited by: Herby, at: 2007/05/29 22:51

Sounds like the battery is a bad one. Check your voltage while the bike is running. It should be around 14v at 3000 rpm.

Hello,had same problems last week. I first checked charging voltage and if battery is good. My bike's voltage was low (taken at the batt terminals with engine running at 3500rpm,reading was 10v -11v,it should be 13.5v-14.5v.) Then checked the wiring from the battery going to the alternator.I found out that the wires from the alternator,the ones that comes out of the alternator cover were all frayed,brittle and cut. I replaced them and had no problems since. There are excellent entries in the archives that you could consult regarding charging problems,if this doesn't fix it.