Hey Friends!
   I have a new puzzler making me scratch my head and I'm hoping you can help.
   My 1985 K100RS began having intermittent trouble starting that is no longer intermittent. When I turn on the ignition, everything is normal. All the usual lights and such. When I press the starter button, the starter does nothing. The fuel pump comes on while I push the starter switch, so I don't suspect a problem in the starter switch. But the fuel pump doesn't stay on for 1.5 seconds as usual. It's only on while the starter switch is pressed.
   I would suspect the starter itself, except that I noticed that the load shedding relay isn't switching. The headlight stays on while I push the starter.
  So I suspected the starter relay, especially since I was starting the bike with a barely functional battery for a while (That issue is resolved. New battery and voltage regulator). So I got a new starter relay and pulled apart the old one. I saw that the points were fried in the old one which I felt confirmed my guess. I cleaned up the points on the old relay to keep it as a spare.
   I just tried putting in the new relay and it made no difference at all. The reconditioned old one didn't work either. I've tried tracing this through on the wiring diagram and looking at the no-start troubleshooting page, but I'm afraid this one might be beyond me.
   Any ideas?

Can you hear the relay clicking in? If you can then check to see if there is 12v at the terminal which goes to the starter motor when you push the start button.

If the relay clicks it's possible that you've connected the two red cables the wrong way round. The battery should go to the screw tab on the right (marked 30) and the starter motor to the screw tab on the left (marked 87).

Okay, I have some additional info:

• The starter relay is not clicking
  
• There is power to pin 30
  
• There is no power at pin 87 at any time
  
• The fuel pump relay is clicking
  
• Load shed relay is not doing anything, headlight stays on (no surprise there, since there's no output from the starter relay)
  
• There is continuity from pin 11 at the ICU pin 85 of the starter relay.
  
• There's 11.8 volts measured from the positive terminal of the battery to pin 85 anytime the ignition is on, no change when the starter switch is pressed
  
• There's 846 ohms from pin 85 to ground when ignition is on, changes to 850 while the starter switch is pressed
  
• There's 6.9 volts going to pin 86 on the starter relay when the starter switch is pressed.
  

  That last point seems the most suspicious to me. That should be 12 volts, right? After work tonight, I'll take apart the switch and clean the contacts. It would be fantastic if that was my only problem.

  Does the behavior of the ICU seem correct? Does it just always provide ground on pin 11? Does it change under some circumstances? Is that resistance a problem? The low voltage? I guess it just needs to provide enough ground to trip the relay, right?

   Thanks for your help, friends.
   -Jon

Dai wrote:If the relay clicks it's possible that you've connected the two red cables the wrong way round. The battery should go to the screw tab on the right (marked 30) and the starter motor to the screw tab on the left (marked 87).

All a relay does is complete an electrical connection.  Which direction the electrons flow shouldn't matter.

I agree. What the h£ll was I thinking of...

Bikesmith wrote:That last point seems the most suspicious to me. That should be 12 volts, right? After work tonight, I'll take apart the switch and clean the contacts. It would be fantastic if that was my only problem.

There is some resistance in the circuit across which voltage is being dropped. That could be the start switch. One way to prove it is to measure the voltage across the switch contacts. It should be close to 0 volts when pressed and 12V when open.

Bikesmith wrote:Does the behavior of the ICU seem correct?

What behaviour is that?

Bikesmith wrote:Does it just always provide ground on pin 11? Does it change under some circumstances?

It provides continuity to ground until the engine RPMs rise above 700, at which time it removes the connection to ground. The reason for this behaviour is to prevent the starter motor from being engaged by the start switch when the engine is running.

Bikesmith wrote:Is that resistance a problem? The low voltage? I guess it just needs to provide enough ground to trip the relay, right?

Correct. The voltage is below the pull-in voltage of the relay. It has to be around 10.5V or more.

Hey Everybody,
   I fixed it! It was the ignition switch. I realized when I noticed that my dashboard lights were really dim that my problem was further "upstream" in the electrical system than I'd been thinking.
   I rebuilt the ignition switch and it was like magic. Not only did I fix the starting problem, but everything is better. The dashboard lights are brighter than they've ever been. The bike starts better than ever. It's fantastic!
  Yay!
  -Jon

Excellent news and thanks for posting your fix.

Karma point to you even though the forum doesn't have them

Jon while I think of this, it is best for the future life of the ignition and handlebar switches to put relays in the headlight circuits because it dramaticly lowers the current carried by those switches to about 2% of what they now carry.
If you search the forum for Eastern Beaver relay you will find how to do it or you may already know but either way it is a good thing to do and it even gives you much better lights.

Great suggestion, Rick! Thanks!
  In the time I've been addressing all the problems on this bike I've also been doing upgrades and making changes to improve reliability. I've already replaced the stock radiator fan with a Spal. Since I live at 5400 feet elevation and will take the bike above 14000 feet but also down to sea level, I replaced the altitude correction plug with a dashboard switch.
  So, yeah, I'm definitely going to wire in a headlight relay. 
 
  Does anybody else have any suggestions for changes to improve reliability or usability on our bikes?

  In one of Chris Harris' videos, he suggests that putting a plug into the end of the drive shaft would keep grease from migrating into it from the final drive splines, lengthening the service interval. Has anyone tried that? Does it work?

  Thanks as always for all your help, friends.
   -Jon

It is a good move to plug the shaft but it's not a critical as many think because the shaft does not move very much on the splines, about 0.1mm if that. The right lubricant and regular servicing is far more important.

Bikesmith wrote:Does anybody else have any suggestions for changes to improve reliability or usability on our bikes?

Engine to battery, positive cable to starter and ground cables. Upgrade them. Easy, effective. 

Great kit, great vendor