Misfire in the Wet? Weak Spark?
Sat under the tank, they tend to get forgotten. But the leads that take the all important spark to the plugs need to be fully-insulated. If moisture gets in where the coil makes contact with the copper-cored plug lead, your 40,000 volts will probably make its way down the side to earth, rather than putting a spark across your plug electrodes. Why? Because it's lazy and wants the easy path. Wouldn't we all?
If you've ever touched a distributor cap, or lead, on an engine with a misfire, you might have felt the same sort of kick. It's easier to find a path to earth through you, than fire a spark across two metal points that are 0.75mm or more apart, especially in a cylinder containing high pressure air/fuel mixture.
The same can be said for the other end where your plug caps are. The rubber sealing boots are falling apart on the GSX's caps, so I'm putting new NGK's on it. For the price of them, it's not worth taking chances.
So what's that got to do with the price of fish?
Well, the original retaining clips for the plug leads had long since made for the hills. When the bike came to me the HT leads were hanging in by the fact that they were completely rigid and couldn't move, and a bit of good luck thrown in. Don't get me wrong, the bike ran fine, but it would have been different in rain.
Later coils did away with the clips altogether, and came factory sealed with a resin of some sort. As much as I would like them to go back together as Mr Denso wanted, without new clips, I'm going to have to seal them in semi-permanently too.