R80 issue

[Basher]

Hi all
I’m helping a family friend with his 83 r80 which has developed an intermittent running issue.
He was having issues with it randomly cutting out then when trying to start it it would backfire and not start, leave it a bit and it would go again.
He replaced the ignition amplifier and no change, I then went through the wiring and replaced some suspect areas and connectors but generally on unrelated circuits but I wanted to clear out a few issues first.
The ignition switch has been bypassed and is just a toggle switch, again I’m not happy with how it’s done and it’s my next job to tidy that but I don’t think it’s the cause.
I stripped the canister and cleaned up the hall sensor which physically looks fine but no way to test. A small amount of oil was found in the canister, while i was there I checked the coils and spark by earthing the centre pin of the connector as the manual says which was all good.
Now if we pull the plugs and turn it over we get spark on each cylinder but when the engine stops turning over there is an untimed spark after which I’m guessing is the cause of the backfire. Would this be a sign of a faulty hall? I don’t want to turn to swapping every part out of there’s a better way to test.
Thanks

[Kurt in S.A.]

Welcome! Could be the Hall sensor. Snowbum might have something on this page on testing:

https://bmwmotorcycletech.info/Ignition.htm

My first thought, though probably not related to the backfire, is the renewing of heat sink paste on the ignition module. If the paste doesn't pull the heat into the heat sink, the module can malfunction.

Kurt

[Rob Frankham]

Probably not the Hall Effect Sensor... Hall effect switches are not known for intermittent faults.

The Electronic Ignition unit used on these bikes has a feature where, if the engine isn't turning (i.e. the unit isn't receiving any triggering pulses) it will switch itself off (after a short delay) until the engine does start to turn again (i.e. the unit starts receiving triggering pulses). When the ignition unit switches off assuming the sensor is in the on position, a single spark will be generated at the plugs. This is a safety feature to protect the ignitin unit and the coils in the event that the ignition is inadvertantly left switched on.

There are a number of other faults that could cause the issue you are struggling with, most of which involve wiring or switching problems, normally involving supply (positive or negative) to the ignition unit of from the unit to the ignition sensor. Another potential source of issues is the igniton unit itself.

FWIW, a go/no go test of the Hall Effect Switch used in the unit is quite easy. The following link describes a way to construct a tester but the circuit used is so simple that it can be assembled for a temporary one off use without any difficulty.

Rob

[SteveD]

Wouldn't have a crack-o-matic coil would it?

Rob...did you forget the link?

[Rob Frankham]

Wouldn't have a crack-o-matic coil would it?

Rob...did you forget the link?

Oops, though I'd included the link... here it is...

https://robfrankham.com/hall-effect-tester

Rob

[Basher]

Thanks
He replaced the ignition module so new heat sink paste is on my list of things to do, il possibly hold the test into but as you say if it’s working and the issue is intermittent then it’s unlikely to show up. Il do some more wiring checks and maybe bypass the feeds and earth on the ignition module and see if it will behave.

[Bob Bennett]

I had similar issues many years back, took a few years to discover the problem but you could look at the crimp lugs on the main
battery cables. They become a high resistance connection/open circuit, could be both ends.

[Basher]

So I went through the wiring again, checked all connections and continuity checks, replaced the heat sink late on the ignition unit and it was still the same.
Ordered a new hall sensor and fitted that the other day and it’s like a new bike, he recons it’s been on the way out for years as it’s running so much better

[SteveD]

Thanks for the update.