Ignition cuts out 91 R100

Symptom: Ignition cuts out when the engine heats up. When this happens the dash lights go out. Bean can and coil are new from EME. Fresh plugs.

Here's a list of what I suspected and fixed. She's still cutting out so I'm at my wits end. What have I missed?
I installed a new rebuild Bean Can. So I eliminate that as a cause. The fact that the ignition recovers quickly also seems to rule out the HES, which typically would stay shut off once heated up.
Suspect the green circuit.
Rewire the green circuit. Bypass the grody white right perch connector and the kill switch. The dash lights now stay on when the ignition cuts out.
Rewire the black circuit. Eliminate the branch out to the PCV solinoids. Assure good ground to the ICU. No change.
Swap out the ICU for a known good ICU. The engine, bean can, coil are at the temp where she cuts out. The bike makes it almost all the way home before the ignition cuts out.
Pull the tank. Put the LED tester on the coil green. Start the bike. Light stays on when ignition cuts out, so it is not the power supply.
I did notice a dip at the voltmeter when the engine stumbled while running. I’ll have to do some more theoretical work. I have ordered a new battery, because sometimes we go all the way around the bend then discover its the battery Even though the volt meter is showing 13+ volts – but that could be the alternator, not the battery. So **** howdy, if voltage is going to the ignition circuit, it should not shut down. What have I missed?

What about renewing the heat sink paste on the ignition module mounting? Usually, failing ignition when engine heats up points to that.

20774 said:

What about renewing the heat sink paste on the ignition module mounting? Usually, failing ignition when engine heats up points to that.

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Thanks. Did that with the "known good" ICU. The one that I replaced was the newer heavy duty type riveted to a big heat sink.

Coil

The symptom sounds like what I had with my 1989 R100GS. 10-20 minutes into the ride it stalled. I had to wait a minute before it fired up again. It was a flaky bean can.

A hint about dash lights and kill switch: the kill switch switches off power to the dash lights

So dash lights off and kill switch on could mean the power into the kill switch failed and hence the dash lights went out.

Did you measure the power on both solenoids at their connectors which are on top of the engine/starter cover?

Btw. what is 'HES'?

/Guenther

Hi Guenther,
HES is the abbreviation used for Hall Effect Sensor.

Yes, coil failure upon expansion has symptoms exactly like that..

To check the ignition I would take a spare spark plug with me. When the motor stalls pull the spark plug wire and insert the spare spark plug and check for a spark.

/Guenther