Intermittent. Any ideas ?

[georgesgiralt]

Hello !
My '82 R65 runs fine. For days. But sometimes, there is a glitch. The ignition seems to  be cut for half a second. The speedo drops about 2000 RPM, the voltmeter shows nothing.
As the ignition harness had damaged wires, I changed it for a new BMW one. Ouch.
The coil is brand new, plugs are new. Plugs caps are BMW and band new (at first I thought it came from the NGK and cheap wires I had).
I tested a new ICU without success.
Carburettors are clean and perfect, ignition is set spot on.
So any ideas or leads is welcome !
Many thanks in advance for your help.

[Barry]

Well it's obviously ignition if the rev counter drops. You already know that.

I'm not sure how the Hall effect sensor could produce a fault like this but logically what else is there  as you replaced or substituted everything else.

[Bob_Roller]

If your voltmeter shows '0' volts during the 'event', you have an electrical supply problem .

The power flows from the battery to the ignition switch, then to the fuses, then to the other circuits on the bike .

My first guess, would be the ignition switch, I've had two fail in the same way over the last 32 years, intermittent electrical loss, then it comes back in a second or two .

[georgesgiralt]

I was not clear in typing. When the glitch happens, the voltmeter shows it's nominal voltage. No drop at all.
So I wonder if the main switch may be at fault ?
Maybe the kill switch ?

[Bob_Roller]

The ignition circuit goes through the kill switch .

One of our members here in the last few weeks had a kill switch go bad, broken solder joint at the switch .

[Barry]

How about monitoring voltage at the +12v terminal of the ignition coil.  The would show whether the intermittent fault was an ignition component fault (indicated voltage did not drop)  or a fault in the part of the electrical wiring , kill swtch etc  that provides the +12 v to the coil (indicated voltage did drop).

[georgesgiralt]

Excellent Barry !
I'll try this. A wire to route to the voltmeter and that's it !

[Justin B.]

I had a similar issue on the '80 R65RS and it was "fixed" by adding a ground strap between the forks and the frame.  Doing a voltage check with the ground lead on the frame and the probe on a 12v point on the bars showed intermittent dropouts when the forks were rotated.

[Luca]

electrical wiring , kill swtch etc

"etc"  --could that include the sidestand safety interlock switch?

[Barry]

"etc"--could that include the sidestand safety interlock switch?

We don't have that on the UK models so I'm not sure. Does it inhibit the starter operation or cut the ignition, You would have to deploy the stand while the engine is running to find out. If I had to guess I would say it inhibits the starter function in the same way as the clutch/neutral switch.

[georgesgiralt]

No side stand switch on my French bike. So something less to worry about....

[steve hawkins]

I have had a kill swich issue on my bike in the past.

The switched can be stripped and rebuilt carefully.  I view the kill switch with so much suspicion that I do not use it ...Ever.

They can break up inside though.

Was here not an issue with standard R65's with head set bearings going as the path to earth was via the forks, through the bearings to the frame?  

I do not have this issue with mine as I do not run any instruments or indicators any more....

Cheers

Rev light

[Barry]

I've heard about the head bearings conducting and never understood what could be going on.  All of the electrical systems on the bars have earth return wires so there would have to be one or more faults for the bearings to become a fortuitous earth path. I've even checked earth continuity between the bars and the frame with an ohm meter and can't see anything strange happening.

The tacho signal feed is the one odd ball that could be at the root of this bearing thing because of the high voltage.



On the kill switch I'm the same and never use it in anger ie to kill the ignition while it's running.  As it's carrying the ignition current of several amps there would be an arc every time it was used which might eventually erode the  contacts. It's the same as opening the points and they arc without  a condenser across them.

[Bob_Roller]

At one time, BMW may have used a grounding or earthing path through the steering head bearings, but if you look at a wiring diagram, all of the circuits that go up to the handle bars on an R65, have a brown grounding /earthing wires that go to the main point somewhere on the frame .

[Speyman]

My vote is with Steve Hawkins. Fiddle with the kill switch but don't lose the tiny parts. Oxidation or deterioration of little bits in the kill switch can cause the ignition to cut out intermittently or just completely die.