Regulator? Contacts?

Got a '82 XJ750 RJ Seca a couple of months ago. About 27,000 miles on it. She's running very well (especially since I put new spark plugs in) but I have a problem with the charging system.

Symptoms:

1. Battery voltage reads 12.07 V with ignition key off. Drops to 11.5 or so with key on, engine not running. With engine running it reads 11.5 and increases only slightly (11.7-ish) with increased rpm.

2. Green alternator wire reads 5.6 V with ignition key on, engine running or not. Increases only slightly (6 V) with rpm.

3. Brown alternator wire reads 10.5 V ignition key on, engine running or not. Increases to 10.8 with rpm.

4. Battery drops voltage pretty quickly with cranking, like after several starts or during the compression check.

Steps taken:

1. Cleaned ground connection, alternator, and regulator connections (the 2-wire and 3-wire connectors and the big connector from the regulator) with a spray contact cleaner and a small diamond file.

2. Cleaned alternator contact rings and brushes. Lots of brush left, about 3/8" to go before the wear lines.

The battery is new, put in just before I bought the bike. One of the first things I did was replace the fuse block.

What's my next step? Can I assume that the regulator is bad, or could it still be contacts somewhere?

 

From what your saying it could be the regulator or a bad battery. If one of the battery cells is bad, it will still register the right amount of volts but lack the required amps to start.

 

Sorry, just saw the (new battery) part. I would think its a bad regulator. :roll:

 

The first thing I would do would be to take a closer look at the brushes. Closely examine their little braided lead wires, that go from the brushes to the connections on the assembly. They can look fine but be all green and crumbly on the inside.

While it is possible that the regulator is bad, it's more likely that something is still not right with the alternator.

You need a manual. The Haynes contains the same info as the factory manual for troubleshooting the regulator/rectifier, as well as the alternator.

And it's always possible it's a connection somewhere. Have you checked on the ground leads from the battery to the frame/motor?

 

I went back in and checked the brush wires.... nice shiny copper. While I was there I checked the rotor resistance at the rings. Only .8 ohms! Spec is 4.5 ohms. Holy cats, how'd I miss that the first time through? Could have sworn I checked it a long time ago.