Think you've hit the nail on the head Rob, the inside of the plug cap is indeed sooty, what next, is there a repaire or send it back to the supplier as its only 6 months old ?
Sent the ignition unit back to the supplier for testing, also got a couple of new plugs, will post the results on here when I've got the ignition unit back and run it again.
I have to admit it was my fault. Seems that I had not got the cooling right in the decathlon and melted the rubber in the top of the plug cap, causeing the problem. Next job is to sort the cooling out.
