85 K100 - bike won't start

[rawhites]

On this sat-for-30-years bike project, I completed the initial rehab work: cleaned out gas tank, replaced fuel pump & lines, replaced steering bearings, front & back brakes, greased splines, new fluids.

Now, to the surprise of few, it won't start. The starter turns, the fuel pump purrs, and the headlight dims when I crank it. But no ignition. The tach barely blips, almost no movement. Maybe I have a spark problem? (I tried the Chris Harris trick of priming the cylinders with some motor oil. Didn't do the trick)

I've ordered a new battery since this one may be defunct after sitting too long over the winter. Off the charger it starts at 13.14V and settles at 12.91. With the key on it dips to 12.47...and drops slowly. When trying to start, it drops to 11.3. And then recovers to 12.3 V....

Once I get the new battery, any suggestions for troubleshooting protocol?

(The clutch is also stuck, but that can wait for another day )

 

[PGlaves]

New Spark Plugs?? Every time I had a K bike not start it was fouled plugs. I always carry a spare set in the tail cone.

 

[rawhites]

Yes sir, spark plugs are brand new!

 

[PGlaves]

Yes sir, spark plugs are brand new!

I would check them again anyway. I suspect oil fouling.

 

[GTRider]

Did the early K’s have a sidestand cutout switch? I can’t remember from the ‘88 I had. If so, that’s a thing to check. I know by ‘90 or ‘91 they did, and that it was possible to crank endlessly—enough to foul plugs—without having any chance of firing up the engine if the sidestand was still down.

Beyond that, you can check spark with a well-grounded external sparkplug (as in strapped to good ground on the bike) and check fuel supply by removing one injector, pointing it into a coffee can or similar, and cranking the engine.

Best,
DeVern

 

[rawhites]

Thanks, DeVern!
It's on the center stand with the side stand up, so I assume that's not the issue.
Once I clean the plugs, per Paul, I'll check for spark. And then will pull an injector and see if I've got fuel flow. (I replaced the lines, but didn't replace the rail or check the injectors)

 

[pauls1150]

As I recall, the early Ks only had 7 fuses, and I don't think a specific one was called out as being in the "ignition" circuit... Have you checked them all?
Does the gear position indicator work properly, and the green Neutral light comes on?
They also had a clutch switch, a tiny pushbutton unit; it should show continuity when the clutch lever is released and open when the clutch is pulled in.
My old Haynes manual doesn't seem to have any info on a sidestand switch, grrr...

 

[rawhites]

Thanks, Paul! I swapped all the fuses, but no improvement.
Yes, the neutral light comes on.
I haven't found the clutch switch, so I can try to look at that too.

 

[51797]

As I recall, the early Ks only had 7 fuses, and I don't think a specific one was called out as being in the "ignition" circuit... Have you checked them all?
Does the gear position indicator work properly, and the green Neutral light comes on?
They also had a clutch switch, a tiny pushbutton unit; it should show continuity when the clutch lever is released and open when the clutch is pulled in.
My old Haynes manual doesn't seem to have any info on a sidestand switch, grrr...

Early K100's had a mechanical sidestand retracting mechanism that used the clutch cable to move an arm that was attached to the sidestand to retract it.
The system was fairly fragile and an unwary person could damage it if the bike is on the sidestand and you tried to pull in the clutch. It wouldn't move and a gorilla type could break the mechanism, stripping the threads on the attaching rod. Many people removed it after some time because without a regular maintenance check/lubrication/adjustment it wouldn't work too well.
It is still operable on my '85.
I don't know when they went to an electrical interrupter.

Frank

 

[AntonLargiader]

The battery sounds OK to me. If it cranks the engine with normal oomph, it's fine.

Motronic models got the electric sidestand switch. K100 4V and all K11.

In no particular order, I would:
- pull the plugs after cranking to see if they are wet
- ground a plug and see if there's spark
- pull the injector rail and see if all four injectors are squirting

 

[pauls1150]

I still haven't found a sidestand switch in the MAX fiche....
But here's a pic from them showing the clutch switch, item 6.

 

[PGlaves]

There is no sidestand switch on K75 and K100 bikes.

 

[rawhites]

The battery sounds OK to me. If it cranks the engine with normal oomph, it's fine.

Motronic models got the electric sidestand switch. K100 4V and all K11.

In no particular order, I would:
- pull the plugs after cranking to see if they are wet
- ground a plug and see if there's spark
- pull the injector rail and see if all four injectors are squirting

Great, thanks! Will run through these.

 

[rawhites]

The battery sounds OK to me. If it cranks the engine with normal oomph, it's fine.

Motronic models got the electric sidestand switch. K100 4V and all K11.

In no particular order, I would:
- pull the plugs after cranking to see if they are wet
- ground a plug and see if there's spark
- pull the injector rail and see if all four injectors are squirting

Hey Anton - wiped the plugs clean again and got a spark in all four when grounded. Yay!

However, after pulling the rail, I don't see any spray from any of the injectors (but confirmed I have pressure after spraying some from the line all over myself lol).

The injectors look like ancient crap....should I even check if they're getting current or just replace them?

 

[rawhites]

Condition of injectors…

 

[pauls1150]

Always verify they're getting voltage (it would be a short-duration square wave, not constant) before spending the bucks for injectors (why buy new ones if the signal isn't there); it's entirely possible you can have the stock injectors professionally cleaned. New O-rings definitely.
The rail may also have junk inside; prob'ly time to R&R the fuel filters (before and after the pump).

 

[rawhites]

Thanks, Paul. The filters, pump, and lines are all brand new. The fuel seems to be getting through the rail okay, but will double check, for sure.
Not sure how to check the injectors for voltage, but I'll search the forums. If you know a good thread about it, please lemme know.
Thanks for the help!

 

[AntonLargiader]

I have actually unstuck those injectors by pressing on the protruding needle tip.

If there is no signal going to them, then obviously that's a different problem. I think the spark control comes from the gray box up by the steering head tube.

 

[PGlaves]

As silly as this may sound my next step would be to unplug the LJetronic ECU, making sure the contacts are clean, and then replugging it in. I once stored a bike that failed to start, rode two-up 640 miles to get a truck and trailer, went to get it, hauled the bike 640 miles back home. Then it failed to start until I unplugged and re-plugged the ECU back-in, only to have it start on the first crank, before I even took it off the trailer. Duh!

 

[rawhites]

I've cleaned both sides of the ECU connector with Deoxit. Hope that's sufficient!
Next step is to test the injectors with a 9v battery & syringed fuel to see if I can get them to fire, and separately check the injector leads with a 12v LED tester.
If there are any other voltage/current tests to do, I'm all ears! Note, to state the obvious: while I have a decent sense for mechanical work, I'm pretty clueless with electrical