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?
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.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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.
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.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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
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
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.
If your bike has the BMW electronic ignition, then the first thing is to inspect the sandy beige colored connector on the pigtail coming out of the ignition "bean can". Take all the proper steps and pull the front engine cover. Unplug that electrical connector set for the ignition, and then thoroughly inspect the beige connector half.
Those connector bodies literally disintegrate during use, which kills the ignition. You can get the new connector from Rick Jones at Motorad Elektrik. It comes already mounted on a pig tail, all you have to do is connect the 3 wires.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for that suggestion. It sounds like a good potential source of the problem.
I was told they did this and didn't believe. Went in to replace the alternator brushes and had to unplug this connector to do the work. The connector literally fell apart in my fingers like a cheap cookie.
Those photos aren't staged.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Update - My connector, unfortunately, was pristine but my Hall sender was not. One Alpha V3 ignition unit later everything is up and running with just a tweak needed to the timing (I'm waiting closer to dark so I can see the marks better with my ancient timing light). Rick Jones was very helpful in getting things right.
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