K75C Electrics

Hi, Wonder if anyone can offer some advice on my '87 K75C which has been showing some odd behaviour recently.

For a while now, I've thought that the battery may be on it's way out. A couple of times, it has felt a bit slow to turn the bike over, and I've taken to using the trickle charger to keep the battery topped up as I'm not that keen on putting a new battery on over the winter months, but would happily do it next Spring.

Regardless of how long the trickle charger is left on for (24 hrs plus), it always feels slightly warm which makes me think that the battery is continuously pulling some current. A good battery will normally charge and then the trickle charger goes cold, so I'm suspicious of the battery.

However, after about 10 days without starting the bike or charging the battery, it started fine and off we went. This has happened a few times now, but I've noticed that the battery light will stay alight for a while after starting and sometimes the bike will just cut out completely. Start it up, rev it, the light goes out and then everything is fine.

This happened again today .... battery light glimmers after starting, bike cuts out, restart, bike now fine go for a ride.

However, whatever it is has now got worse. After a 20 mile ride, I stopped for a few minutes, then tried to restart.

Ignition OK, bike turns over but won't start. Try again - bike now won't even turn the engine over. Ignition off. Ignition on, bike turns over and starts, battery light shines brightly when running, bike stalls. Repeat cycle.

Eventually I managed to start the engine and keep it going until the battery light went out and then it drove home fine, but once in the garage I have the same problems. It will start, but the battery light stays on and then it stalls etc.

Have taken the battery out and and had a look at the brushes on the starter motor ( the root of most electrical problems) and though they look worn, I'm pretty sure they are long enough. Commutator looks much like every other one I've seen.
Battery is showing 12.4 volts on the bench.

I'm confused ...... thanks.

You may be experiencing problems with the voltage regulator (internal to the alternator), or the brush contact rings.
I purchased a new regulator for my '95LT only to find when I started to replace it in the alternator that the slip rings(contact rings) that the brushes ride on was too dirty for the brushes to conduct sufficient current. Thus the reason it wasn't charging enough.
Polished the rings, and replaced the regulator anyway since I had it apart(and it came with new brushes as well), and all is well.

I'm guessing that yours being a '87 is probably the 400 watt version, I can't say one way or the other if your regulator is as easily replaceable as the newer larger ones, but I would think it would be close.

Thanks for the replies. I have just replaced the brushes in the starter motor (they were beneath the lowest length value in the manual) and am about to put the starter motor back into the bike and try it.

Have read on the internet that when the brushes are worn, the load shedding relay is always in the "load shedding" position, so that would tie in with what I was seeing where the battery charging light refused to go out when the engine was running.

Will let you know how I get on when I put it back in and try it.

Well, I've put it back together and tried it and I have exactly the same problems.

I've checked the resistance through the starter motor brushes and its 0.1 ohms at any point, so that's all good.

Symptoms are:

1. Bike will start normally and tickover.
2. Battery charging light can either be off, glimmering or glowing brightly.
3. When off or glimmering, bike will carry on running.
4. When glowing brightly, bike will run for a few seconds and then stop suddenly.
5. When this happens, starter motor will not then turn the engine over, although fuel pump can be heard running when start button is pressed.
6. Turn off ignition, starter motor works again and same symptoms.

I have propped up the fuel tank and removed the load shed relay and tested this on the bench with a 12V supply. Relay correctly clicks and contacts can be seen to make and pass current.

I have connected a volt meter across the battery terminals and when off, it shows 12.7V, and when the bike is running, it shows 13.9 volts regardless of the state of the battery charging light, which makes me think that the alternator is fine and that the load shedding relay is doing its job.

I am now very confused ......

12.7 Volt battery tension after just shutting off is normal for a good battery. after some time it will likely drop off to around 12.5 Volt.

Charging at around 13.8 to 14 Volt is also normal, so it appears that the alternator, voltage regulator and the battery seem to be OK.

During the starting - the starter motor actually running - a voltage drop to something approaching 11 Volts is also to be expected.

It sounds like there is a current leak to frame/ground somewhere???