electrical issues 1982 yamaha xs 400

I recently bought a 82 xs 400 r seca. cleaned out the carbs, new gas and fresh oil. new battery and it was running great. about five minutes into riding, the bike dies, and the battery voltage goes down. the battery is brand new, the brushes in the charging system look fine. any ideas on where my problem might be? please let me know if any of you guys have run into this problem. thanks. -Lane

 

If battery voltage drops, I would say the charging system is not fine.

I had issues with an xs400 I was working on, the guys on the xs400.com message board are well versed

 

Hello Lane & welcome to the forum.Sorry to hear you're having problems with the bike you just got. A few questions first, that will help diagnose your problem. You mention a new battery-was it fully charged before installing it in the bike? Is this a recurring problem or a one time thing & is now parked ? Did you try charging the battery and try again? Maybe some history of the bike. Are you working on it yourself or taking it to someone? It could be a battery connection or a lot of other things. Reply with everything you think might be important to know.

 

i bought the bike a month ago and have been slowly working on it myself. i've only ever had a gsxr track bike so this style is new to me. I started with all new fluids and fully cleaning out and syncing the carbs. it runs great for a short while and just dies. the battery is brand new and the bike has been out only 4 times. the 3rd time it died a mile from my house. i brought it home, charged the battery back up, and took off again. this time, i let the bike idle for a couple minutes and then made it about 2 miles when the bike cut back out. my buddy has an xs 650 and said he had that problem before, so we checked the brushes in the alternator which was his problem, and they looked good. i'm now stumped. thanks for the help.

 

Make sure you know what good brushes look like... I know I would only be making a haphazard guess at looking at them, and can imagine someone wrongly judging them. Who knows! Just be sure.

Definitely sounds like your bike isn't charging the battery, though. I would try charging up the battery, get it running, and set the revs (adjust choke) to put it at maybe 2.5k or so (get a fan if this goes on more than a couple minutes if you're enclosed or anything, it's an air cooled engine so it needs air), and measure your contacts, see if the generator is providing anything. That should help isolate it.

I'm no expert on electrical, though, so if no one else gives an idea, go for it--otherwise wait for someone to confirm the method I just made up or do some research on the forums, use the search bar up there. Lots of good stuff saved up around here.

 

Yeah, fintip is right. Check the voltage at the battery when the bike is running @ around 2500-3000 RPM. Should check out at around 13.5-14 volts. Also check around to find the ground strap & make sure it has good connection.

 

As above, should be around the 13-14 v range at 2500 rpm and up .,
If not, your reg/rect unit is toast..... And double check those grounds...
I killed my reg/rect with a loose one......

Other things to look at are all your safety switches, relays and the ever evil fusebox.
Also possible is a voltage leak somewhere, check all the connections at your controls and in the headlight bucket "ratsnest"