Advice Needed 1987 r80rt

[asotorobles]

Hi there, I am new to this forum and need your help with advice.
Bike starts and after 10 seconds it dies. I must wait hours to start it again and works fine.
I replaced spark plugs, cables, ignition module, ignition coil, diode. It worked fine for a while but now, I am feeling frustrated with the same problem now that is cold over here.
I thought about the hall sensor, but I want to have input for some more wise than me people.
I really appreciate your time to this matter.
Stay and ride safe. Hope the pandemic is not that harsh on you all.
Regards.

[SteveD]

Welcome.

One thing at a time I s'pose. This isn't mine, can't remember where I got it from?

BMW ignition tests.

To test coils and ignition module
Pull a spark plug, insert it back into the plug wire cap, and ground it securely on the cylinder jug.
Turn the ignition key to ON. Place the kill switch in the RUN position. Now, watch the plug while flipping the kill switch on and off.
You should get a spark as the switch is turned off. If you DO get a spark, this indicates that both your coils and your ignition module are functional and you can focus on the ignition sensor.

To test ignition sensor (bean can)
remove negative cable from battery, remove front cover to access bean can.
Remove a spark plug and ground it to engine as in 1 above.
Find the electrical wire that leads from the bean can upwards to connect with the main harness. Disconnect that connector by carefully removing a thin wire bail that holds the two halves of the connector together.
Pull the plug apart. Using about a 3” length of thin wire, insert an end of the wire into the MIDDLE female hole of the three-hole connector that leads to the bike's harness (not the remaining half of the connector that's made up to the beancan).
Connect negative ground to battery. Turn on ignition to bike. Place kill switch in Run position.
Now, while the thin wire remains inserted in the middle female connector hole, strike the other end against the metal alternator cover as though you're striking a match. If, when you "strike the match" you also get a spark on the grounded spark plug, your hall effect sensor has failed.

Are the starter jets in the carb bowls clear? Be surprised if that was it but it's a small quick thing to check.

[Rob Frankham]

Two suggestions...

1) When you fitted the new ignition module, did you renew the heat sink paste between the module and the heat sink... the modules are designed so that, should they overheat, they will switch off to protect themselves. I wouldn't expect this to happen that quickly but...

2) Since the issue is intermittent, simple tests of the hall effect sensor are likely to give a false reading. That being said, it's quite easy to do the test if you have a few wires, a LED and a resistor. This link is to my webpage on how to build a tester but the circuit is so simple that you can do it on an ad hoc basis without most of the hardware... https://robfrankham.com/hall-effect-tester. In this case, though, the best test would be to substitute a known good unit, ideally by borrowing one from someone who has a spare. (I do have a spare, but since I'm located in the UK, postage would put it out of the question...)

Rob

[gspd]

I would be inclined, based on the symptoms described, to suspect a faulty/intermittent hall sensor.
In my experience, these hall units, which were also widely used on german cars of the era, tend to function intermittently before totally quitting. It is not uncommon for them to quit when hot, only to start working again after cooling off.
Their failure rate is quite low. I suspect that 95% of our old bikes are still running on the one they were born with, even after decades of use. However, unlike points, which can be serviced in a motel parking lot, when your beancan dies, you're stuck.

Rob, love your tester! brilliant!
Correct me if I'm mistaken, but I seem to recall a way of testing hall sensors with a simple analog multimeter.
A VW/Audi/Porsche dealer I worked for had 'the official' Bosch tester, undoubtedly more complicated and expensive than yours, but it did the same thing. Unfortunately, no tester can diagnose an intermittent problem unless it's happening at the exact moment that you do the test, and none can get you going again when a hall unit failure is confirmed.

I always carry a spare beancan (and coil, and module) on long trips, but so far I have never needed them.
Something to do with Murphy's law, I suppose.

[Rob Frankham]

Rob, love your tester! brilliant!
Correct me if I'm mistaken, but I seem to recall a way of testing hall sensors with a simple analog multimeter.
A VW/Audi/Porsche dealer I worked for had 'the official' Bosch tester, undoubtedly more complicated and expensive than yours, but it did the same thing. Unfortunately, no tester can diagnose an intermittent problem unless it's happening at the exact moment that you do the test, and none can get you going again when a hall unit failure is confirmed.

I always carry a spare beancan (and coil, and module) on long trips, but so far I have never needed them.
Something to do with Murphy's law, I suppose.

Yes, you can do it with a multimeter (analogue or digital) If you simply omit the LED from the circuit (connecting the resistor between wires 1 and 2) keeping the rest of the circuit as is, then use a meter to check the voltage across that resistor, it will switch from near zero to near battery voltage as the bean can mechanism turns. You could even do it with the whole thing connected on the bike using an insulation piercing probe to make contact with the signal wire(2) and turning the engine but I don't like this approach for two reasons:

1. I don't like piercing the insulation in this sort of appplication... It will probably allow moisture into the wiring and cause corrosion and
   
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2. It is reliant on the other ignition components to ensure a meaningful result which could complicate matters.

I built the tester to be a simple plug and play, go/no go tester. It's not foolproof but the chances of it giving a false reading are very low. The other use, of course is as a simple 'timing light' when setting initial static timing on reassembling the ignition systems to the engine. Again, something that can be done by other means but having a simple PnP solution is nice.

I've been thinking about designing the 'other half', a PnP unit which will allow the testing of the rest of the ignition system but I keep running into the old 'design concept' issue of a mutating spec making the thing too complicated... One day I might get there...

Rob