stalling and visible spark

hi,
after a jet wash last week my bike was running really poorly. the front cylinder was cutting out at low revs. at first i thought i might have been water that had gotten into the front plug. i removed the wire running into the plug and all seemed perfectly dry. but a week later it was still intermittent.

i've just been out investigating further and noticed a spark from the plug wire to the engine itself (closest point is the rubber cover just at the bend in the wire). spark corresponds directly to the stutters in the front cylinder.

this is however only present at idle. i've shifted the wire slightly and seems to run ok but im sure it will just swivel around again while im on a ride.

what can i do to remedy this or is this a normal phenomena???

is it harmful to the bike in anyway?

thanks

plug wires deteriorate over time. Yours needs replacing!

Really a common problem this. Try a good dousing with WD 40 or similar.

You've got something conductive - salt, water, crud, who knows! - around the plug cap assembly. Just dousing with WD40 will displace any water pretty effectively, but not necessarily the crud. There is no substitute for taking the plug out, disassembling the cap from lead, cleaning everything and then using some good hi-temp silicone grease all over it as you reassemble (sources done to death on this forum). You don't need masses, just a good smear. Make sure the little drain hole is clear, and Bob's your Auntie.

Cleanliness is everything.