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Topic-icon Cripes a 1974 R90s that won't start.

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7 months 2 weeks ago #4329 by exbritmorgan3
Cripes a 1974 R90s that won't start. was created by exbritmorgan3
Hello from Northern California . No smoke in the air...no one around the house with a list of must be done type chores . I was looking forward to a quiet afternoon doing an oil change. I have had the bike for about 7 months and it has behaved perfectly.Although I have changed plugs, oil, filters and fixed other small cosmetic or slightly bodged areas its always been a pleasure to work on. .It is an honestly presented motorcycle , well known locally it has probably close to 75,000 miles but has always been taken care of. It's been a wonderful experience considering everything else I have ever owned has been unreliable and thrashed i.e. old british bikes or poorly assembled old italian singles always gave me trouble and seem like poor decisions and the sign of a wasted youth.

In my mind with my bmw. I finally have reached the promised land of vintage airhead ownership.

However this afternoon after I unplugged the battery from the tender and turned the key and press the starter button nothing happened. .
Finally the bike is stored in a garage..it's not heated but the area I live in is pretty temperate and it was working 30 days ago.

Any advice from the readers will be helpful.. (Sorry if this question has been asked before...just refer me to the right spot on the forum.)

Here are the symptoms.

1) The ammeter is pegged..and I do mean pegged against the negative (far left) portion of the gauge.
2) The bike is in neutral but the neutral light is not lit.
b) There are no lights working on the console except the high beam indicator (blue) light when on high beam.
3) There is no tick/click from a solenoid.
4) The signal lights will not work
5) The headlight does work
6) There is power to the coil from the ignition.
7) There is no spark at the points
8) The battery is fully charged (I checked voltage across the terminals) and the new battery (3 months) has been on a tender.
9) There are two in line fuses both are intact
10) The prior owner replaced the troublesome fuse block with an upgrade, I am not sure which firm's.


IS there a fuse link or master relay that I am missing? As there was power to the coil from the ignition switch I felt that this must be working.

Thanks in advance. (also please don't tell my wife I have another motorcycle in pieces in the garage.)

Cheers,
Julien

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5 months 3 weeks ago - 5 months 3 weeks ago #4468 by Wobbly
Replied by Wobbly on topic Cripes a 1974 R90s that won't start.

exbritmorgan3 wrote: Here are the symptoms.
1) The ammeter is pegged... and I do mean pegged against the negative (far left) portion of the gauge.


The fact that the ammeter is "pegged" denotes that you have a short circuit somewhere in the bike's electrical system. Just like water taking the quickest way to the ocean, electricity will take the shortest, most direct path back to the battery. So the reason nothing else is working is because all the power is busy taking the easy way home.

Did you by any chance remove the front engine cover to inspect the points or alternator brushes ? If so there is a very high probability that you smashed some wires between the engine and cover during reassembly. If not, then think back about other work performed. Problems very rarely appear from nowhere. No disrespect to you, but the issue is most likely related to work you just completed.

Hope this helps.

Don't hide 'em, Ride 'em !!
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Last edit: 5 months 3 weeks ago by Wobbly.

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5 months 3 weeks ago #4476 by murphyam53
Replied by murphyam53 on topic Cripes a 1974 R90s that won't start.
When an R90S, one of the most beautiful bikes BMW built, won't start, the forum should leap into action. Let's try to figure this out. I am using my Clymer manual, 1973-74 R90S, schematic for reference.
Addressing the symptions:
1. BMW equipped your bike with a voltmeter, not an ammeter. The unenergized position for a voltmeter is fully left (zero volts). The unenergized position for an ammeter is in the middle, so it can swing left (drawing current from the battery) or swing right (pushing current into the battery i.e. charging). With the key in the on position, the voltmeter should read battery volts. If it doesn't, bad or no connection to the battery. The voltmeter is powered from the ignition wiring but fused. Check the green wiring, fuse and connections in the headlight bucket.
2. The neutral light is on the same fuse as the voltmeter.
2b. The high beam indicator light is unfused power from the ignition switch. All of the other console lights are powered from the same fuse as the voltmeter.
3. The starter solenoid is powered from that same fuse in the green/black stripe wiring. Are we starting to see a pattern?
4. Signal lights, same fuse.
5. The headlight is unfused.
6. The ignition power is unfused. It is only switched on with the ignition key.
7. This one doesn't fit the pattern. How are you testing for spark at the points? If there is power to the coils from step 6 there should be power to the points. If the points are closed, opening them (like with a small screwdriver) should produce a spark at the plugs. If the points are open, bridging them momentarily should produce a spark.
9.& 10. Check those fuses for continuity, clean and tight connections. The upgraded fuse block is a wild card in this troubleshooting process. Some pictures of the installation would help.

I'm a retired electrical engineer so I understand the trouble shooting process and can respond quickly to any questions. Let's get this beautiful bike back on the road. Here in Minnesota (currently 5 degrees with a howling north wind) , working on problems like this is the only way to get my motorcycle fix.

Andy MOA #15601

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5 months 3 weeks ago #4480 by murphyam53
Replied by murphyam53 on topic Cripes a 1974 R90s that won't start.
Julien,
I just had a thought. If you don't have a schematic for your bike, here is a web page for one. freewiringdiagram.blogspot.com/2016/12/b...-wiring-diagram.html
Any electrical problem can look hopeless without a schematic.

Andy
ABC #15601

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5 months 3 weeks ago #4485 by exbritmorgan3
Replied by exbritmorgan3 on topic Cripes a 1974 R90s that won't start.
Andy,
thank you so much for your very helpful advice and exhibit! Well you were spot on. So check this out...
The prior owner somewhere back in the depth of time had created a set of inline fuses and a remote fuse block that had blown fuses...I replaced the fuses in the block and in line (where blown) and still had problems. I removed the ferring , headlamp and turn signals and found that the original fuse block was still in place...with a blown fuse! Ok replaced the fuse...Eureka everything worked! Put it back together and then blew another fuse (yes...I know I was using magical thinking to assume that I had fixed the problem.) Took it apart again and then stared at it for a while , probed with circuit tester and figured out that the wiring on the brake switch had been improperly "fixed" and was grounding on the frame. Ran new wire...put everything back together (after checking everything still worked including voltmeter working) took it for a ride..50 ft later short circuit. Pushed back to garage took everything apart..replaced fuses. Everything worked perfectly...put bike back together went for a ride used turn signal. Blow fuses ...ok took it apart and figured out that the way the left turn signal bowl had been put together when everything was tightened up it shorted. Ok fixed that!!! Put everything back together signal lights work perfectly phew fixed...Not exactly...took bike for a ride went over some bumps then short circuit ...fuse blown. Ok figured out after taking everything apart again found out that the voltmeter had a busted mounting post that would periodically short out when going over a bump. Yes...I think I figured out finally why there were so many remote fuses. Anyway onwards and upwards! I now have the tach at international speedo because it was making a sound similar to a boeing 707 getting ready to take off.
Anyway still loving the experience of riding a BMW! Also the community is great . I owe you a soda and a pizza the next time you are in Northern California.

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5 months 3 weeks ago - 5 months 3 weeks ago #4487 by Wobbly
Replied by Wobbly on topic Cripes a 1974 R90s that won't start.
"Remote fuses" were one of those owner "upgrades" that was highly suggested back in the 1970's. My bike came fitted with them too. I removed enough owner installed wire from my RT to fill a paper shopping bag !

Funny how most of these upgrades take longer to trace and repair, than simply leaving the bike stock and repairing the bike per the owner's manual.

Don't hide 'em, Ride 'em !!
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Last edit: 5 months 3 weeks ago by Wobbly.

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