I believe my '81 R65 has a faulty Hall sensor. It seems to die in the hot summer while I'm in stop and go traffic and run fine in the cooler Fall/Spring. Also idles very high (2-2.5K rpm) once the engine is hot. My usual fix is to pull over and wait for it to cool down and then drive it home once the traffic has cleared. It has a newer ignition module and a brand new Dyna brown coil.
Do you have a ballpark figure for servicing bean cans? Some suggest just buying a new one or the Alpha unit rather than go for a "rebuild" on the OEM unit.