Stalls coming back to idle - electrical gremlin

[thecableguy]

I'm trying to get my head around this problem.  It's definitely electrical in nature. As I describe the symptoms you'll see why I've come to this conclusion.

Background: 1986 K100RT I bought about 2 months ago, been riding nearly every day and am tooling up for major work like spline lubes, new front tire, rear rotor etc. over winter. Bike was ridden by previous owner, and hasn't sat (other than during Wisconsin winters), and has always been garaged.

A problem has cropped up in the last week and I'm looking for some info on what to look at first.

Once the bike is warm, sometimes when coming to idle after riding at speed, the motor will just quit.  Often I am still rolling, so popping the clutch will get it turning again.  If not hitting the start button will. 

If it happens a couple of times in a row (like when I'm pulling into the parking lot at work) the electrical nature will show itself.  It will die, and the dash will go blank. No lights, even the clock LCD segments will disappear.  If I turn the ignition off, the clock digits will reappear.  When it's "latched" in this failure mode, turning the key, even just to the parking light position, will kill the segments on the clock and no lights will light.  I haven't had a chance to have a meter with me when it's happened, but starting today I'll start carrying one around.  I'd like to see what the battery voltage is or if it changes when this happens.  Battery is strong and starts the bike with no issue otherwise, charging system is keeping it charged.

Just letting it sit will clear the electrical "latch" and turning the key works as normal and the bike starts and runs fine.  Until I ride for awhile and it starts happening again.

I thought it might be too low an idle speed, so I rode around today with the "choke" on, holding the idle at around 1400, but no, it still exhibited the issue.

I know the usual suggestion would be to clean the ignition switch, but that really doesn't make sense in this case.  Flipping the key back and forth has no effect, and why would it exhibit it just when going back to idle?

I've searched the forum and only found one post talking about a similar issue, but there's no resolution I can find. http://www.motobrick.com/index.php/topic,5710.0.html

Any suggestions?  TIA for all your help!

Jim

[The Mighty Gryphon]

Do a search on cleaning a K bike ignition switch.  The the intermittent shutdown and panel blackout are some of the symptoms when mine was dirty.

[thecableguy]

I guess I'll give that a try tonight when I get home.  As one well-versed in electronics, I'm having a hard time understanding how that could only cause an issue after the bike is warm and only when coming back to idle.  Could the load-shed relay be an issue?  Randomly activating at low RPM and sticking sometimes?  But no, you can still crank with the load-shed relay activated, that's what it's for...

Confused in Madison

[Martin]

Had the same symptoms with my Brick. Turned out to be a loose connection on the earth lead on the back of my non standard isolator switch. I would check battery connections on both battery leads for cleanliness and tightness.
Regards Martin.

[thecableguy]

That's an easy one.  Thanks Martin, I'll try that tonight as well!

Jim

[Laitch]

I've searched the forum and only found one post talking about a similar issue, but there's no resolution I can find.

There's a lot more than that one. Among them there is this one and there's also this one.

[The Mighty Gryphon]

Coming to an idle or coming to a stop?  Coming to a stop will cause compression of the front end and g-forces to reverse on things like the wiring harness changing the direction of the stress loads on wiring connections.  There are also resonances as the engine speed winds down that can also affect things. 

As far as the ignition switch the contacts do not have a lot of force making the connection.  My problems occurred both when starting/turning the switch on and when riding it would shut down and start again a moment later or when I turned the switch on or off.  Took me two months to find the problem which it turns out is not all that rare.

[thecableguy]

Coming to idle.  I have reproduced the issue while at a stop by revving the engine then dropping to idle.

Odd, huh?

[Brad-Man]

You might want to check your TPS for proper operation.

I believe it should signal the efi that throttle is closed...

[Laitch]

I'm trying to get my head around this problem.  It's definitely electrical in nature.
Flipping the key back and forth has no effect, and why would it exhibit it just when going back to idle

If you haven't sorted this, the problem might have a different source. Read about this rider's similar problem and his remedy.

[thecableguy]

So far, so good...

As the initial suggestions were to check the battery connections and clean the ignition switch, I did just that. 

The negative lead attachment to the trans did have some corrosion, and the hex head stripped on me trying to remove it.  Cleaned up the area with DeOxit and 1200 grit emery cloth. Replaced the bolt and used copper anti-seize when reassembling.  The rest of the connections I'd already looked at when I pulled the starter a couple of weeks ago.

Disassembled the ignition switch and gave it a thorough cleaning with the same DeOxit and emery cloth.  Had some carboned-up areas, but didn't look all that bad.  Reassembled with a tiny bit of grease on the moving parts and a dab of the fiancee's nail polish on the set screw.

Rode it all day yesterday trying to reproduce the failure.  Never reared it's ugly head.  Not going to ride much today, family obligations and crappy weather, but tomorrow I'm taking her over to the Slimey Crud Run so I'll get some more miles (and opportunities to fail) then.

If it does come back I'll dive into the additional suggestions by Brad and Laitch.  But for now, wish me luck!  I'll update again in a few days.

Thanks again guys, this forum has an incredible wealth of knowledge...

Jim

[Laitch]

Rode it all day yesterday trying to reproduce the failure. 

Now there's a unique fund-raising venue. The MOTOBRICK.COM Ride To Reproduce Failure.

[thecableguy]

Now there's a unique fund-raising venue. The MOTOBRICK.COM Ride To Reproduce Failure.

I'll start going door to door, lining up donors...  "Help us eradicate this failure from the Brick community forever!"

[Martin]

 :2thumbup:
Martin.

[stokester]

Now there's a unique fund-raising venue. The MOTOBRICK.COM Ride To Reproduce Failure.

I'm in, let's go to Mad City!

A transplanted Cheesehead in Virginia.

[thecableguy]

So I'm ready to call this one fixed.  Ran all day today and she never even hinted at stalling.  On the other hand, the entire Slimey Crud Run got to enjoy hearing a K with a slipping sprag clutch...  That turned some heads I'll tell ya!!

Jim

[Martin]

 :2thumbup: More than likely the earth lead due to the fact you lost all power including the clock which points to total power loss. You don't loose the clock with a faulty ignition switch. Now go ride it.
Regards Martin.