About to try to fix my 1985 K100 - it starts cutting out after it's hot and won't start again (maybe 30 mins into riding).

What I've done:
- replaced the Hall Effect sensors
- replaced the rubber air intakes
- replaced internal and external fuel lines

My plan of action based on various advice I've gotten & reading the forums is:
- check exhaust valve clearance
- test temperature sensor
- see if my coils are the original black ones (if so I guess replace them - although the orange ones are expensive!)

Does that seem like a sound plan of action? Any other thoughts or advice?

If you haven't, you definitely want to check valve clearance, especially the exhaust valves.

Check eBay for coils.  There can be some good deals there compared to buying new.  Having said that, it is odd that both coils would quit at the same time.  I think there is an ignition control module under the tank that may be giving you a problem.  I have no experience troubleshooting that.  Maybe someone else can help you there.

Did you replace the hall sensors with new or just use an old plate. Did you test the hall sensors because what you describe is absolutely classic of those things.

I see you have a bit of warm weather in Austin. Maybe worth putting fresh thermal transfer paste under the ignition module, that can be quite heat sensitive.

Point-Seven-five wrote: I think there is an ignition control module under the tank that may be giving you a problem.  I have no experience troubleshooting that.  Maybe someone else can help you there.

This was the exact problem of Jumpinjimmy.
When the engine was at temperature, the ignition module was cutting off its signal to the fuel injection computer.
When the engine was cutting off, the ignition was still working but the fuel injection was failing. The ICU was failing to send the proper signal (pin #8 ) to the EFI (pin #1).

The way we found it was by having a strobe light on one ignition lead and LEDs on the injector plug.
When the engine was ready to quit, the intensity of the LED on the fuel injector started to fade then stopped. At no point the strobe like had a miss.

Another question is: When the engine stop, if you cut the ignition, does it starts again or do you have to wait that it cool down?
If the engine start again, I would check the ignition switch.

RicK G wrote:Did you replace the hall sensors with new or just use an old plate. Did you test the hall sensors because what you describe is absolutely classic of those things.

I did replace them with new sensors (that I put on the old plate). I soldered to the wiring harness by the sensor, is it possible the wires could get iffy when heated up by the tank?

Crazy Frog wrote:

Point-Seven-five wrote: I think there is an ignition control module under the tank that may be giving you a problem.  I have no experience troubleshooting that.  Maybe someone else can help you there.

This was the exact problem of Jumpinjimmy.
When the engine was at temperature, the ignition module was cutting off its signal to the fuel injection computer.
When the engine was cutting off, the ignition was still working but the fuel injection was failing. The ICU was failing to send the proper signal (pin #8 ) to the EFI (pin #1).

The way we found it was by having a strobe light on one ignition lead and LEDs on the injector plug.
When the engine was ready to quit, the intensity of the LED on the fuel injector started to fade then stopped. At no point the strobe like had a miss.

Another question is: When the engine stop, if you cut the ignition, does it starts again or do you have to wait that it cool down?
If the engine start again, I would check the ignition switch.

When it cuts out I can usually start it again a time or two, and then it seems to run when revved high but cuts out when revs drop. Then it will cut out and not start again until it has been fully cooled down.

My guess is coils. YMMV

duck wrote:My guess is coils. YMMV

A couple coils questions:

Is there any way to test coils, or does one just get replacements and pop 'em in and see if it fixes the problem?

If you look up the K100 troubleshooting PDF it has some resistances to test on K100 coils.

Not sure if that relates directly to your issue though.

Without ruling off the coils, I would more be inclined to test the water temperature sensor before replacing the coils.

The idiot light should illuminate and then the radiator cap should blow before it shuts down. (Does the L-Jet have a temp-based shutdown programmed into it?)

The reason I guess coils is that a local guy had the shut down when it gets warm issue on his 85 and after I swapped in a set of coils that cured it.

Hello All , my bike had a cutting out problem as well in severe heat , it turned out to be loose battery cables expanding in the heat , worth a look

John Re

Melbourne Australia

duck wrote:The idiot light should illuminate and then the radiator cap should blow before it shuts down. (Does the L-Jet have a temp-based shutdown programmed into it?)

The reason I guess coils is that a local guy had the shut down when it gets warm issue on his 85 and after I swapped in a set of coils that cured it.

The 2v Ks don't have shut down on overheat. All they have is that overheat prevents a restart until the engine cools down. I do wonder that because I overheated the 92 LT one day in traffic and it restarted with no problem.

111°C is when the light comes on and 113°C is when it wont restart. If you shut it down when the light comes on the radiator will thermo syphon due to cooler coolant in the radiator and the engine probably will even out in temp in a fairly short time and not get to the 113°C mark.

Crazy Frog wrote:Without ruling off the coils, I would more be inclined to test the water temperature sensor before replacing the coils.

You're talking about this sensor right - http://www.euromotoelectrics.com/TEMPSENS-K197-p/tempsens-k197.htm 

(and not the in-the-radiator valve...)

timz10000 wrote:You're talking about this sensor right - http://www.euromotoelectrics.com/TEMPSENS-K197-p/tempsens-k197.htm 
(and not the in-the-radiator valve...)

Yes this is the water temperature sensor.

I've successfully tracked down heat related problems by using crushed ice wrapped in a cloth used in conjunction with a heat gun. Once the bike cuts out pack crushed ice around suspect parts and see if it starts up if it does then hit the part with a heat gun. Keep trying various suspects until you find it. You can also try using Freeze spray instead of the ice.
Regards Martin.