Electrical system stopped

[Fatmandu]

I was trying to tune my carbs, then my electrical system stopped, as if I had turned the key off. It did this to me last night, so I checked the fuses, and they were all intact. I disconnected the battery after I couldn't figure it out, and left for it alone for the night. This morning I connected the battery, and everything came back on as if nothing had happened. So I started the bike again, and started trying to set the idle so I can sync the carbs. The engine would die as I was adjusting the idle, so I would start the engine again and continue adjusting. This happened a few times, until I hit the starter button, and everything died again as it did last night. I checked the fuses again, and they are still fine. I have power to the ignition switch, but no lights or anything. Could this be the regulator/rectifier failing as everything gets up to temperature? Has anyone had a similar issue? Any info would help.

Thank you

 

[Fatmandu]

I guess that I could add that this is a 1979 CB750K

 

[CMAbbott]

Had a similar issue with my 82 CB750F. Sometimes it would crank sometimes nothing happened when I pushed the starter button. There was a loose wire (brown) in the connector to the ignition switch. I could push it over with my finger and the push the button then it would crank. Also noticed that it would shut off while I was working on the bike. It was that pesky wire the whole time. Hope this helps.

 

[Fatmandu]

Thank you, CMAbbott. I will check that out.

 

[amc49]

The switch CAN give issues and worse if someone has replaced it, the bottom electrical section is molded of plastic so flimsy they often come slightly apart to open circuits up.

 

[Fatmandu]

I tried this again today and I got the same results, as I assumed would happen. I tried wiggling the brown wire, and still nothing. I opened up the housing on the starter switch and there is no corrosion or loose wires. I heard from a co-worker that when relays get old, they will shut off when they get hot. Has anyone else seen that happen? And if so, which relay could be causing this?

 

[amc49]

There's only like one relay on the bike.............unless you count the flasher. That relay only for starting and has nothing to do with motor staying running.

If battery old then just it or cable connection issues. Check your grounds and by that I don't mean simply look at them, or worthless.

 

[Fatmandu]

So, I think that I have this figured out. The regulator/rectifier was bad. When I was researching replacements, I learned that a common reason for the regulator/rectifier to fail is a bad stator rotor. So I tested that, and it was also bad. I have now replaced the regulator/rectifier the stator and rotor. The bike now runs, gets up to temperature and I was able to sync my carbs.