[ChrisCurvyS]

I'll get a pic tonight Sid. I don't think it's too wide though as it's clicking into the plug as it should - instead I think it's too long, from the top to the socket the plug fits into.

I suspect a well-meaning mechanic friend who did some work on the bike a while back has replaced the HT lead and cap together (I vaguely remember him saying something about the former). He probably used a cap he had lying round the workshop, not noticing that it was sticking out a little bit behind the radiator.

IIRC there was a long dry spell after he did this but the problems with the rain and dampness started soon afterwards.

Oddly, when the bike's been left in the shed and not used for a while, (rather than left in the rain) it will actually start on both cylinders but start misfiring on the front after a few minutes. Could it be that moisture is accumulating in the bottom of the plug well because of the loose cap, then when the heat starts to come through it's evaporating up into the bottom of the cap and causing it to short?

Or is that complete tosh from the mind of someone who got a D in physics GCSE?