I did notice though that if you look at the gap inbetween the top of the tank and the bottom of the top headrace, there is a channel in the top of the frame. I did a little test with a syringe of water, and the water runs down this channel... and drops straight onto the l/h mounting post of the coil where the earth connector is, and also hits the connector on the coil that sparks!
There's also a strip of sponge around the front edge of the tank that I suppose is there to stop vibrations. I made that wet (as would happen if the bike stood in the rain all day). Once the sponge became waterlogged, the water was draining down that channel - and onto the connector and earth connection!!
So I removed the coil and took all the melted amalgamating tape off (it melted cos I sprayed it with damp-start last time
) and taped it up again PROPERLY. I also covered up the offending connector itself and once the coil was attached back onto the frame I covered the l/h post too. So now all that is visible is the positive connector; I say positive cos the wire is red 
Having re-connected all the battery connections, I started her up and squirted water all over the covered connection and the bike didn't stutter once. 
Just before putting the airbox back on, I emptied an ice cream tub (raspberry ripple with bits of cake in it...yummy
) and cut a strip (about 5 inches wide) ot of the bottom of it. I taped this plastic to the front of the airbox up under the sponge with gaffa tape so that when the airbox was replaced it hung down in front of the coil like a shield. Tested it with the syringe and the water ran down the plastic and didn't go near the coil 
Hopefully this is the end of the problems. I dread to thing what a mechanic would think if he saw it. It's a definite bodge job, but just maybe its one of mine that actually works!!!!
