Lost power than died after 1hr of riding

Hi all,
Hope someone can help with this, tried searching but not coming up with the same issue: (I'll use miles and km as i'm Aussie but I realise most on this site are American)
Rode my '81 XJ750 55km (half an hour at 65 miles per hr) to a nearby town on the weekend, dropped something off and about 2/3 of the way home I noticed blinkers barely working, seemed to be struggling for electrical power. Around the same time bike started running rough, struggling to stay at 100kph (60-65 miles an hr) and gradually getting worse until I pulled over and stalled close to home. Wouldn't start, seemed like a flat battery.
It had stopped outside a friends place so I left it for a couple of days, and after sitting there it started and rode fine the few km back home?

Something getting hot? Battery not charging? Any help would be much appreciated guys.

 

Also, that was about the longest ride I've taken on it, and the battery is fairly new.

 

1. Does it have the original fuse box?

2. How much fuel was in the tank when it stalled?

3. Have you ever cleaned the fuel tank vent?

 

Thanks for your reply k-moe

1. No, previous owner has replaced it, I'll take a pic later and post it.

2. Fullish, over 3/4

3. No, I haven't. Previous owner got rust out of the tank, I haven't touch since.

 

dnardy,

Remove the connections from the batter and put the batter on for a good charge. While it is charging check the following.

1. Check the new fuse box and make sure with a multi meter that you have good connection through the fuse's
(while you are checking the connections below keep a close look out for wire that have been cut, worn from rubbing that could have shorted on the frame and open wires)
2. The grounds need to be looked at, remove the bolts and clean the surface area that the bolt or washer is touching and add some electrical grease.
3. Connectors for all the wires should be gone over if they have not been done already. Carefully take apart the plastic connectors and check them for green corrosion, clean them if you can and then add the grease.
4. After the maint above have been completed put the battery back in and try to start her back up. If all is well then you will have have to check the charging system.

Hope this helps.

 

I'd put a multi meter and check to make sure your altenator is charging at 2k should have 13.5 volts + if it is not you are running on the battery if it drops below 11 volts things start to shut off like the TCI . It is possible sitting a few days voltage went back up enough to start and ride again . But this would be a good starting point. If you are running a wet cell battery service with distilled water to proper level. Unless you are running a gel battery then not much to check there. Cheers

 

I'd also vote charging system. If just one of the 3 phases from the stator aren't being rectified, you can get a bike that will run for a fairly long time before being DEAD electrically. The bike is literally running off the battery until it's drained. Happened to a buddy of mine a couple of weeks ago.

The spec is for the voltage to be maintained at 14.3-14.8 volts above 2500 rpm. Above 5000 rpm, you should see the voltage regulated no higher than 14.8V.

Electrosport has an excellent troubleshooting diagram, but you'll need to check the wiring (3 white wires from the stator, and green and brown from the rotor, and the red wire coming from the R/R plug. If you see any burning or melting on the connectors, you'll need to repair it.

 

Thanks for all the advice. Looks like I've got some investigating to do on the weekend.