Hi Jg - my R65 died on me in exactly the same way just 45 k's after I bought it. It turned out to be the OEM coil just died. I had it replaced by my then local dealer and 5 years later it died again. It seems that these OEM coils have a limited life I eventuallyfound out from BMW shop. I bought an after market coil from them about 10 years ago and it's still running okay. If it turns out to be the coil then maybe find a quality aftermarket unit instead of the OEM unit. Good luck finding the fault mate ....
Adrian - I think you have a 1984? If so, you have electronic ignition and indeed your OEM coil was a bad design by BMW (or Bosch). In fact, it earned the nickname "crack-o-matic".
jg has a 1980, which is a points ignition and two separate coils. My original coils were still working great when I replaced them 5 or 6 years ago "just because".
Like Bob mentioned, my front coil mount broke off the main frame a long time ago, taking the main ground connection with it.
jg - check that connection and make sure that it is clean, and that the coil mount is not getting ready to fall off.
Take your ohm meter and check for continuity between that point and the negative terminal on the battery.
Besides the big fat positive wire going to the starter, there is a small positive wire that is hooked to the battery. Make sure it is in good shape.
Disconnect the ground wire on the battery, and then remove the front engine cover and look around.
And you might want to consider a preemptive relocation of the harness ground, for the day that the front coil mount DOES break.
Here is how I did mine:
Remove the paint on the bracket and use dielectric grease (or even Vaseline or axle grease) on the connection.
These bikes will run on only one cylinder, and even start on only one, so it is unlikely that both carburetors were affected simultaneously. As long as you have fuel in both bowls, you should be OK there.
It is also possible that the condenser that hangs on the side of the bean can failed. If you decide to replace it, don't throw away the old one until you are certain that that was the problem. It is always good to have an old working one for backup.
Have you checked / measured your point gap and condition of the points since you got the bike?
Feel free to remove the bean can from the bike to make this chore easier, but you might want to use a Sharpie (pen) to mark the position of the bean can before removing it so you can get your timing in approximately the right spot when you put it back.
