Started up the valver in the morning and she was "missing" slightly on throttle..
Anyway drove for about 5 minutes and it wouldnt stop doing this, opened the bonnet on the hardshoulder and heard this crackling..
Ther was sparks jumping between the 2nd sparkplug and inlet manifold??
I cleaned up with a cloth and wedged the rubber sideways and this stopped it.
Whats the cause of this? Moisture buildup?

Do i need to replace the plugs??

ta in advance!