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Topic-icon r80/7 motor quit

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3 weeks 4 days ago #3887 by colin
r80/7 motor quit was created by colin
shortly after a high speed (85 mph) run, my motor suddenly quit. i have a 20 amp inline fuse on the red wire going to the ignition switch. the fuse was blown. i had a spare and replaced it. the engine fired right up. i patted myself on the back and started to drive off and the engine went dead again. i had a 7.5 amp fuse and tried that just to see what might happen. again the engine fired right up, idled, and also would rev up smoothly and quickly when i turned the throttle. started to drive off and the engine died again. battery is good. any ideas?

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3 weeks 3 days ago #3905 by Wobbly
Replied by Wobbly on topic r80/7 motor quit
I suppose you're home now....

Turn OFF or disconnect everything. Replace the fuse with an ammeter. As you SLOWLY plug back in various lights, horns, and accessories one-by-one, at some point the ammeter will go crazy. The short is in the last item you re-connected.

If you haven't replaced your LH light switch to be able to turn the lights OFF, then you may need to simply remove bulbs.

Slow and steady wins the race.

Don't hide 'em, Ride 'em !!
#15150

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3 weeks 2 days ago #3912 by colin
Replied by colin on topic r80/7 motor quit
thank you for your reply. i will elaborate on my blown fuse issue. with ignition turned on, all lights and horn function perfectly. when i then press the starter button, the motor cranks and the 20 amp inline fuse on the red wire to the ignition switch blows. does this indicate a bad starter switch or a short in the wire to the starter switch? or other possibilities? just looking for a more educated opinion than my own.

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3 weeks 2 days ago - 3 weeks 2 days ago #3913 by Wobbly
Replied by Wobbly on topic r80/7 motor quit
Other ideas....

► There are generally 2 paths to allow power from the positive side of the battery to flow. They are sized and connected for very specific jobs...
1) There is the large 12ga RED wire that runs from the battery to the starter switch and then on to the ignition sw. This handles all the power for ignition and lights.
2) There is the extra large 4ga wire which connects the battery to the starter terminal.

If the 4ga wire was unable to handle the current required by the starter, then it might be "back tracking" somehow through the smaller 12ga wire. I have never seen this and I don't understand the routing, but your symptoms describe something like this.

On BMW motorcycles it is quite common for battery corrosion to crawl under the jacket of the Pos battery cable and pop out at the starter terminal. This corrosive action eats up the entire cable inside the jacket of insulation where it cannot be seen. The only signs are a "bloom" that looks like regular battery terminal corrosion at both ends of the cable.

Photo: Battery Cable Corrosion

Most people never take the starter cover off until the starter stops working, so they have no idea this corrosion is under way.

► Is your starter original ? And if "Yes", then have the bearings inside the starter ever been re-packed ? At 30-40 years of age the grease in the starter bearings starts to solidify, causing the starter to pull more current. I have one pal who claims this oxidized grease is the major reason for starter burn out. You might want to pull your starter and re-pack the bearings and bendix with a synthetic grease.


All the best.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 3 weeks 2 days ago by Wobbly.

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3 weeks 2 days ago - 3 weeks 2 days ago #3915 by 1872
Replied by 1872 on topic r80/7 motor quit
Since the fuse originally blew while the engine was running and subsequently cranked and idled without blowing the fuse, I disagree, it is a starter problem. Wobbly give good troubleshooting information.
Initially you stated the bike idles and only blows the fuse only when attempting to drive away and then later state the fuse blows when the engine cranks. If the former, I would look for a loose wire or a strand of wire shorting to the frame only when the starting to move.
Good luck troubleshooting.

Bob
Last edit: 3 weeks 2 days ago by 1872.

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2 weeks 5 days ago #3934 by DocP
Replied by DocP on topic r80/7 motor quit
I'm in something of the same boat with my 1983 R80 RT. After a 25 mile run and a couple of local errands, I pulled to a stop sign and the engine quit. I restarted and it ran for about 2 seconds, then quit again. Since then, it will crank, but shows no sign of starting. Everything seemed fine until it quit. All I can think of is a loose connection in the ignition circuit, but everything seems to be okay. Any suggestions will be appreciated.

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