My 2000 'cat started running rough last spring after it came out of hibernation (I run it once a month or so through winter). I've replaced filters and plugs with no joy, and had carbs balanced

Today removed coils to test and to of the plug caps are 12k Ohms instead of 10 (the other two are just over 10). Would this be enough to cause problems? (The coils and leads appear to be spot on)

Two years ago I fitted a new exhaust (Motad pipe, Fuel 'can) and took it from Cumbria to South Wales and back with no problems, but I suppose it might have worked loose. Another possible problem?

Any suggestions?

I'd suggest cleaning the carbs myself, you might be delving too deep. You could also try sticking some V Power in it and giving it a good spank for a tank or so

Yeh the carbs could do with a ultrasonic bath,,  varnish builds up  if not used regularly ,  esp with this fuel nowadays ,. i know there a pig to remove on a 4cylinder ,😬