'87 K100RS no start

[motodude]

The bike was running fine earlier today. 

The bike is fairly new to me and I'm still checking things out. I noticed the Batt. light on the instrument cluster was not lighting up when the key is turned on, so I tested the charging system and found that it was not charging.  So, I pulled the alternator.  Took it apart, cleaned it out.  I checked the brushes, both are well within the limits (one 10mm the other 9mm).  Cleaned the slip rings.

The PO put a new battery in it.  I think I'm finding out why now.

I put everything back together.  Batt. showing 12.6 volts and--although the charging system was not working--it _was_ starting just fine.

Anyway, engine turns over very well.  I hear the fuel pump running just as it should (I replaced the fuel filter a couple of days ago).  Everything lights up (except for the Batt. light) when I turn on the key and goes dim when I hit the starter button.  But, no joy. 

I did "move" the wires running down the RH frame tube when removing and replacing the alternator.  I visually checked them and they all appear unmolested.

I think it is not getting spark as it does not fire at all.  But, I don't know everything about these electrical systems.

What should I check next?

Thanks,
Tom

[Inge K.]

About charging: since the the warning lamp doesn`t function, have you checked the bulb?

If the bulb is blown, the alternator won`t charge. To test the bulb and the circuit, remove the connector at the alternator and ground the thin blue wire.

If the bulb is blown, it`s importent to use the correct wattage (3W) to get the charging functioning correctly.

If the bulb and the circuit is found to be OK, you probably need a new voltage regulator.

Inge K.

[motodude]

Thanks Inge.

I vaguely remembered some connection between the bulb and charging but could not recall exactly what it was.

I was going to replace the bulb but thought I'd check the charging system first which led me down the road I took.

I'll get to it tonight, after work.

Tom

[frankenduck]

If the bulb is blown, it`s importent to use the correct wattage (3W) to get the charging functioning correctly.

This isn't 100% correct.  I've got several tens of thousands of miles running LEDs in there (WAY less than 3W) and the charging system works fine.  The one caveat though is that you have to rev the bike up to 2,000 RPM or so after starting until the warning light goes out. (indicating that the alternator circuitry has been "excited" enough.) Once that warning light is out, everything works fine.  (If you just start the bike and let it idle with that light on then you're running from the battery.)

[motodude]

Thanks for the information, Drake.

I performed Inge's test and no light.  So I pulled the instrument cluster and tested the bulb (it was not obviously, "blown") it didn't light by itself either.

Tomorrow, I'll goto Ripoff Shack (easier to get to than the dealer) and see if I can get some bulbs.

I also put the battery on the charger today but it still spins w/o firing.  Still not sure whats up with that.

Tom

[frankenduck]

Just so you understand how the charging light works:

One side is connected to the battery (switched circuit).  The other side is connected to the alternator. (blue wire) When you turn the bike on, the battery side is at 12V and the alternator side is at 0V so the bulb is lit.  When you start the bike and the alternator is working it puts the alternator side of the bulb up to 12 for a net voltage difference of zero across the bulb that makes the light go out.

(The 12V figures are nominal, not actual, voltages but you get the idea.)

[motodude]

My understanding is such:
When I turn the key on, the switched circuit (as you call it) puts 12v to the bulb and the alternator side is grounded, allowing the bulb to light up and energizing the winding (or armature?) in the alternator allowing it to energize/charge.

If the bulb is burned out, the alternator is not energized and does not generate/charge.

I was not aware that the alternator put 12v back to the bulb once it is energized/working, thus turning the bulb off.  Maybe that's why I'll sometimes see a dim glow on that bulb when using the brakes.  The brake light draws some of that 12v (from the alternator) down allowing  for a differential in voltage and the dim glow?

Thanks for the information, every little bit helps.  Now, if I could just figure out why the engine does not fire.   ???

[motodude]

When discussing the dim glow on the batt. light, I'm referring to my K75, where the bulb and charging system works.

Tom

[motodude]

Okay, I pulled a plug to check for spark and it sparked quite well.

I pulled the #6 fuse and there was power at the hot side.

I got a pressure tester and when put in-line it bounced back and forth from about 35 to 40 psi.  My understanding is that 36 psi is the correct value for this test. 

I also pulled an injector electrical connector and placed a 12v LED across the terminals.  I got a flash when I first hit the starter button and another when I let off the starter button.  But none in between, when holding down the starter button.

So, its got spark, it's got the recommended fuel pressure to the rail, but I'm not sure about the LED, I would expect it to flash continuously while holding the starter button but it didn't.

I pulled a couple of the injector electrical connectors and checked the voltage while cranking.  I got about 11.3 volts.  But, it didn't matter which of the two wires I tested, I still got 11.3 volts.  My understanding is that one of them goes to the FI computer which momentarily grounds/closes the circuit, opening the injectors.  Could the wires be crossed somewhere?

Anyone have any ideas?  Wires crossed?

Thanks,
Tom

[kennybobby]

i doubt the wires could be crossed since you said it was running previously.

There are several sensor signals to the L-Jetronic box that need to be checked and verified.  For example if the engine temperature sensor is not working then the fuel injection will be shut down.  Maybe the connector to that sensor was dislodged when you were messing with the wiring harness.

There is a good troubleshooting and diagnostics flowchart at this site:

http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm

Let us know what you find.

[motodude]

There are several sensor signals to the L-Jetronic box that need to be checked and verified.  For example if the engine temperature sensor is not working then the fuel injection will be shut down.  Maybe the connector to that sensor was dislodged when you were messing with the wiring harness.

There is a good troubleshooting and diagnostics flowchart at this site:

http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm

Thanks KennyBobby,

I've been using that site to aid in troubleshooting.  It is a very nice resource.

Other than the Alternator, Battery, FI computer & injectors, I haven't been messing around w/ the wiring harness (tank is still on the bike for example, hiding all the relays, etc) but I get your point. :-)

I will take your advice and start looking at the inputs to the FI computer.  Apparently, they're expensive. :-)

Other feedback I got suggested that the LED should flash continuously, indicating something wrong with the FI computer, its connector or inputs.

Thanks again,
Tom

[motodude]

Well, I pulled the tank and cleaned some of the connectors under there.  Put it all back together and it started.  I'm kinda bummed that I didn't find exactly what was wrong.  That way I'd know I fixed something.

Tom

[johnny]

every time i see a my motobrick wont start thread i know it is something simple... now ride it till it wont move... yeeeeeeeeeeeeehaaaaaaaaaaaaaaaaaaaaaaaaaa...

j o

[ReneZ]

Did you clean the grounds under the tank? Without a proper ground the ECU can switch the injectors all day, but lack of ground won't allow them to open.

[motodude]

No, I did not clean the [main] ground under the tank.  I recently had the tank off and that particular ground apart and cleaned when putting headlight relays in the bike.  You are correct that grounds are very important.

I kinda suspect it was the main FI computer connector.  I did spray some contact cleaner on that plug and let it evaporate overnight before plugging it back in.  Also, the latch for that particular connector appears to be defective.  I'll probably see what I can do about fixing that.

On the plus side, the batt. bulb lights and the charging system works.  Which is what I was doing when this whole, "no start" thing started.

[DRxBMW]

I kinda suspect it was the main FI computer connector.  I did spray some contact cleaner on that plug and let it evaporate overnight before plugging it back in.  Also, the latch for that particular connector appears to be defective.  I'll probably see what I can do about fixing that.

My K 75 whip stopped running last year for NO apparent reason.

At first, I suspected a BAD load of petrol. After dumping the old gasoline and R&R with fresh NO change.

Upon close inspection, turned out the ECU somehow was slightly un-clipped and loose. Once reconnected properly, BAM she fired right up.

Whenever there's a intermittent engine problem double check the ECU connection.

FWIW, a conductivity enhancer works far better than electrical cleaner for the ECU plug & pins. Staiblant 22 is my favorite but there a less expensive routes to go. Rail Zip, DeOxit, whatever. Even NAPA offers a enhancer.

http://stabilant.com/llsting.htm#rrevv01.htm

[motodude]

My K 75 whip stopped running last year for NO apparent reason.

At first, I suspected a BAD load of petrol. After dumping the old gasoline and R&R with fresh NO change.

Upon close inspection, turned out the ECU was somehow was semi un-clipped and loose. Once reconnected properly, BAM she fired right up.

Whenever there's a intermittent engine problem double check the ECU connection.

FWIW, a conductivity enhancer works far better than electrical cleaner for the ECU plug & pins. Staiblant 22 is my favorite but there a less expensive routes to go. Rail Zip, DeOxit, whatever. Even NAPA offers a enhancer.

http://stabilant.com/llsting.htm#rrevv01.htm

I inspected the ECU but did not clean or really touch its connector.  The engine was getting good spark so I didn't suspect anything there.

I was unaware of these "conductivity enhancers".  I'll look into them as I really don't want this sort of thing to happen again.

Thanks,
Tom