Author Topic: K100 electrical issue  (Read 599 times)

Offline tannerman917

  • Curious
  • Posts: 4
K100 electrical issue
« on: February 26, 2019, 10:38:18 PM »
Hi, apologies for the incoming stupid question.

I've got my '85 K100 almost to the point of running (all new fuel lines, oil/coolant change, confirmed good spark/compression) and was getting impatient while sending my fuel tank off to be acid dipped at a radiator shop to clean the inside and give me that nice aluminum finish on the outside.  I really wanna hear this thing start, so I went to give it a crank without checking over everything first... I hit the starter, but had a dangling accessory plug that was bolted to the coil pack cover ground off somewhere around the coils, I heard a small click and the clock died.  Now whenever I turn the key to the on position, the LCD clock fades out, none of the dash lights up, and it doesn't make a sound.  I've checked all the fuses, and they appear to be good.  Is there a relay I should be checking, or am I SOL without tons of troubleshooting?

Thanks in advance for any assistance.
  • USA
  • '85 K100 RT

Offline The Mighty Gryphon

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  • Posts: 4536
Re: K100 electrical issue
« Reply #1 on: February 26, 2019, 10:58:43 PM »
Welcome!  Has your bike been converted to a cafe racer?

It sounds like you have a switched short circuit that is draining the battery when the ignition is switched on. 

I would suggest charging the battery and putting a voltmeter on the battery terminals.  Pull all the fuses out and unplug the headlight.  Turn on the ignition and watch what the voltage does.  One at a time put the fuses back, switching on the ignition and watching the clock and the voltmeter. 

Each fuse connects another load to the battery, lowering the voltage slightly.   If a fuse causes the voltage to drop drastically, note which one it is and pull it out and continue with the rest until all the circuits have been connected through their fuses.

When you're done let us know what you've seen. 
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline The Mighty Gryphon

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Re: K100 electrical issue
« Reply #2 on: February 26, 2019, 11:04:57 PM »
One other point, the accessory plug is usually connected directly to the battery.  It may or may not be fused. 

Check it's wiring very carefully, making sure that there are no bare spots in the wire that can touch the engine or the frame.

It's not uncommon to have the starter relay weld the contacts when you try to start with a low/weak battery.  Is the starter trying to turn or get hot?
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline lysy40

  • Motobrick Curious
  • Posts: 16
Re: K100 electrical issue
« Reply #3 on: February 27, 2019, 12:50:23 AM »
Check starter brushes.
  • Poland, Bytom
  • 1988 k75s, 1987 k100lt

Offline daveson

  • ^ Proficient Motobricker
  • Posts: 442
Re: K100 electrical issue
« Reply #4 on: February 27, 2019, 01:52:11 AM »
Also, if you're lucky, starting from the source, maybe you shorted a cell of the battery, reducing it to 10 Volts.

The fuses might not have blown, but may be cracked, which sometimes can't be seen.

Has earth to the battery failed,  that is 12 volts from battery to frame (it's not the strongest looking earth strap) and just keep following the trail.
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline szabgab

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  • Posts: 338
Re: K100 electrical issue
« Reply #5 on: February 27, 2019, 04:28:37 AM »
The fuses might not have blown, but may be cracked, which sometimes can't be seen.

+1 to that.  This exactly happened to me yesterday,  fuel pump fuse gone some distance from home.  Checked fuses,  especially number 6, and everything looked to be OK.  Pushed bike home swearing,  I remembered to swap fuse 6 with a new one only at home,  surely enough bike started straight away.  I wish I saved myself the sporting afternoon and done this on the spot,  so worth trying to check them first.  If no-go,  do Gryphon's method,  which is the best way to try troubleshooting anything electrical.
  • Budapest, Hungary
  • K75S 1985 model

Online Laitch

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Re: K100 electrical issue
« Reply #6 on: February 27, 2019, 10:29:17 AM »
  I really wanna hear this thing start, so I went to give it a crank without checking over everything first... I hit the starter, but had a dangling accessory plug that was bolted to the coil pack cover ground off somewhere around the coils, I heard a small click and the clock died.
Consider that your battery is weak and not holding a charge. It doesn't matter if it is new. New products can be defective. Battery tenders only charge batteries up to the level of their capability to hold a charge but they won't charge a discharged or defective battery. Don't attempt to charge a low battery when the temperature is at freezing or below.

Batteries in good condition installed in motos that are ridden infrequently can be preserved by the simple means of disconnecting the battery's negative terminal at the transmission after the moto has been well-ridden on an outing. The battery in my moto is six years old. The day I put it on the lift for winter storage I take it for a long, lonesome ride then I put it on the lift and disconnect the negative terminal from the transmission. I don't reconnect it until I go for my first spring ride unless I've performing some modification that needs the battery's input.

The battery always starts the moto six months later. I will consider replacing it this year.
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline tannerman917

  • Curious
  • Posts: 4
Re: K100 electrical issue
« Reply #7 on: August 14, 2019, 09:39:47 PM »
So sorry for not bothering with any of the responses before now, but thanks for all the suggestions! 

Since the last post, I've gotten the bike running when the issue magically disappeared, but I never actually figured out a solution and it has since reverted to its non-running state.  I have looked at the starter relays, and they are not welded open but sometimes they stick or the solenoids inside click around depending on the state of the battery charge.  I find that the top 7.5A fuse draws the most power, unsurprisingly.  I still need to dive in with a meter and see what the voltages are doing on each of those circuits.  I have also removed the starter and cleaned the brushes/commutator, but I will need to order a set of brushes as the ones I've got are getting too short.

In order of the questions you've asked:

Welcome!  Has your bike been converted to a cafe racer?

No, I was originally planning to do that (I know it's unoriginal but I wanted to machine the rear suspension from the Retrorides bike as a school project) but have since found a Honda CBX that will be taking all the funds not necessary to get this thing running and riding so I have a bike in the interim.  Sorry K guys, but that inline 6 was too sweet to resist 😍

One other point, the accessory plug is usually connected directly to the battery.  It may or may not be fused. 

Check it's wiring very carefully, making sure that there are no bare spots in the wire that can touch the engine or the frame.

It's not uncommon to have the starter relay weld the contacts when you try to start with a low/weak battery.  Is the starter trying to turn or get hot?

Also, if you're lucky, starting from the source, maybe you shorted a cell of the battery, reducing it to 10 Volts.

The fuses might not have blown, but may be cracked, which sometimes can't be seen.

I know the starter relay is being a bit finicky, but I'm not sure if that's due to something else in the chain.  The battery is happy at 13.1v, but I should probably replace that top 7.5A fuse.  When everything in the cluster dies, the whole bike just quits.  No noise from the fuel pump, nothing from the starter.  As of late whenever I try to start the bike, I've had it on a tender/charger.  I turn the key, center the kill switch and hit the starter.  One click from the Ebox, clock fades and lights die, and it won't do a thing before I turn off the ignition and let it sit for a few hours.

I appreciate all the help from you guys, and I've really got the kick in the pants to get this thing done now that I have a few weekends/nights with some time before the really nice fall weather rolls around in November here in ATL.  Hopefully I'll have it running soon!  If there's any other suggestions I'll try to be a bit more responsive this time.
  • USA
  • '85 K100 RT

Online Laitch

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Re: K100 electrical issue
« Reply #8 on: August 14, 2019, 11:19:07 PM »
Clean and tighten the battery's negative ground connection on the transmission. Clean and tighten the battery post connections. Clean the multiple ground connection mounted to the frame backbone beneath the tank. Clean and tighten the ignition switch connection under the tank. Try starting after each of those tasks so if it starts, you'll know why it started.
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline tannerman917

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Re: K100 electrical issue
« Reply #9 on: August 17, 2019, 04:46:09 PM »
Clean and tighten the battery's negative ground connection on the transmission. Clean and tighten the battery post connections. Clean the multiple ground connection mounted to the frame backbone beneath the tank. Clean and tighten the ignition switch connection under the tank. Try starting after each of those tasks so if it starts, you'll know why it started.

Thanks for the advice!  I'm back at it this afternoon and have done a little more troubleshooting.  I had a meter to the freshly cleaned battery terminals, and when I went to start the bike it went from 13.1V to 300mV and stayed there... I have determined the clicking I though was coming from somewhere in the relay box is actually in the starter.  I had already determined the brushes are pretty much shot, they're fully extended and look like they're still short.  I think I'll check on that o-ring that billday was having issue with a couple of years ago, maybe my issue stems from a combination of that and short brushes.  Will report back soon!
  • USA
  • '85 K100 RT

Offline Martin

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  • Posts: 3797
Re: K100 electrical issue
« Reply #10 on: August 17, 2019, 06:21:50 PM »
Szabgab there are options for the standard blade fuses. I am running ones with a built in LED that lights up when the fuse fails. I also have resettable circuit breaker fuses on board to aid in diagnostics if stuck on the side of the road. Unfortunately  they are too high to fit under the OEM fuse cover but they can be used if the cover is omitted.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Online Laitch

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Re: K100 electrical issue
« Reply #11 on: August 17, 2019, 06:50:25 PM »
. . .  maybe my issue stems from a combination of that and short brushes.  Will report back soon!
The starter in these motos is a key component for reliable electrical performance. The starter acts as a ground; a dirty starter causes electrical whack. A starter with worn out brushes needs a thorough cleaning and its brushes replaced. Consider that as your next move. Tutorials are on the site.
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline tannerman917

  • Curious
  • Posts: 4
Re: K100 electrical issue
« Reply #12 on: August 18, 2019, 01:18:57 AM »
Succeeded in getting it running today!  I had to pull the starter out once more and manually zap it back to life, but after doing that and resetting that little o-ring it fired right up!  However, I was stupid and thought I might be able to get away without replacing the boots on top of the throttle bodies... they're much worse than I thought and almost certainly are what's keeping the bike from idling right or responding to throttle input.  Are there any more resilient options out there?  I thought a short piece of intercooler-type piping would work well with the silicone on the outside, but I doubt I could find any that would fit both the 40 and 42mm ends.
  • USA
  • '85 K100 RT

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