" Any suggestions as to why an 1100GS should cut out in rain?. I've been offered the bike for not too much cash but want some idea of whait I would be looking for. "
Mine does a simillar thing. After standing out in the rain it starts ok but then will often missfire very badly or cut out all together. Once cut out it will at times refuse to start for quite some time and the l/h injector clicks continuously and the fuel pump runs non stop.
Had mine cut out last week on way home from work in a downpour(oh yeah before i get told off 1996 1100), problem was water in the fuel tank connector on rhs under the plastic cover. drained out , sprayed with wd40 and been fine since.
Bear the problem could be something as simple as that.