'78 Yamaha XS400 electrical issue

[Ian522]

Let me start off by saying hello, I am new to the forum and just purchased my first bike, a 1978 Yamaha XS400, after taking the MSF safety course. I bought it with the intention of fixing it up and knowing it would need a little TLC, but I am trying to figure out where to start.

The bike doesnt want to start using the electric starter. It cranks (although weak) and turns over, but wont fire up. However, it always fires up using the kick start, usually on the 2nd kick. Once it is running, the lights are very dim at idle. But when I rev it up the lights get brighter like they should be.

Could this simply be due to a weak or dying battery? Or is it something more serious like an igniton or other electrical problem, etc...

I would apprieciate any insight.

[BuzZz]

It sounds like a power supply problem at first guess, alright. Have you charged or checked the voltage of the battery? Or had it load tested? A new/good battery hooked up to clean and tight connections at all pionts up to the starter will probably get it starting better.

It's the best place to start looking anyways...

[flynrider]

I would start with the battery. There's a fine line in battery power where it has enough to run the starter, but the starter's drain on the battery means that there's not enough power left over to drive the ignition system. The result is exactly what you experience. Using the kickstart works fine, but no start with the electric starter. The weak cranking is also another tipoff.

The question would then be, "Why is the battery weak?". If it's an old battery, then it could be past it's useful life. I would bet that this is the case, since you comment that the light get bright when you rev up the engine. That's usually a good indication that your charging system is functioning.

On my old bikes that had a kickstart, it was common for me to use the electric start until the battery was too old to provide enough power for the start. Then I'd use the kickstart and get a couple more years of life from the battery.

[Ian522]

Thanks for the advice.

The battery is so dead now that the lights barely switch on, starter wont even crank at all, and even the kick start wont fire it up. But I did find a local dealer that will sell me a battery, filled up and charged for $49. Is that a reasonable deal?

[flynrider]

That's a pretty good deal, especially from a dealer. I usually pick mine up at K-mart and they run around $35-$40, but I have to fill it and charge it myself.

[noodlenoggin]

+1 on the battery advice.

Also, you should check your generator brushes to see if they're worn down. If the XS400 is like my XS650, they're really easy to access, under one of the engine sidecovers. Your Haynes or Clymers manual should have pictures.

[Ian522]

thanks for the advice, ill check out the generator once I get the service manual(should come any day now). As for the battery, Im picking it up this afternoon from the dealer and ill put it in and see if she fires up.

[Ian522]

just to update, I just put in the new battery and she fired right up! Lights are nice and bright too. I sure am relieved that it wasnt a more serious problem with the electrical system.