You have explored most of the avenues mentioned, but I'm still wondering whether it is the ECU/ICM heat sink issue, which doesn't show itself unless/until the module overheats - 32 years old, hot weather &/or a very hot airhead engine.
This is the theory. Beneath the tank, the Ignition Control Module is fixed to a mounting bracket that acts as a heat sink, with a bond of thermal conducting paste, aka heat sink compound, as the filling in the sandwich. With age & heat cycles, the paste fails, crumbles away, leaving a minute air gap, which the allows the module to overheat, typically cutting the spark completely, shutting down the bike suddenly whilst riding. Once the module cools down, maybe after only 5-10 minutes, the bike can then be restarted, sometimes with a hefty backfire due to unburnt fuel that has collected in the exhaust.
It has to be worth a look for peace of mind. This is some top end thermal paste from the IT world - others are readily available.
This is the theory. Beneath the tank, the Ignition Control Module is fixed to a mounting bracket that acts as a heat sink, with a bond of thermal conducting paste, aka heat sink compound, as the filling in the sandwich. With age & heat cycles, the paste fails, crumbles away, leaving a minute air gap, which the allows the module to overheat, typically cutting the spark completely, shutting down the bike suddenly whilst riding. Once the module cools down, maybe after only 5-10 minutes, the bike can then be restarted, sometimes with a hefty backfire due to unburnt fuel that has collected in the exhaust.
It has to be worth a look for peace of mind. This is some top end thermal paste from the IT world - others are readily available.
