I put the bike into the garage last saturday and rang up today for an update. Carbs and clearances and the MOT. It seems that the last owner or mechanic was a complete tit. The plugs were loose - the crush washers weren't tight and it seems that 80% of the engine heat in combustion transfers through the washer into the porcelain. Not in this case and the plugs were bloody hot. So much for the last bike shop doing it properly (the receipt shows it at less than 2000 miles ago, last september).
The mechanic also says that the cams are pitted through the last owner not changing the oil or using cooking fat instead of good stuff! Not too badly, he says - but it needs to be kept on top of. I change the oil religiously and use 10/40 magnetec.
The really good news - the clearances were sooooo tight they were virtually nil. All in all, quite a surprise considering the last owner said he looked after it. Twat!
Its running much better now and I expect it back soon for some cuddling and a heated garage. So, now I have a better idea of why it ran poorly. One day, I will own a bike from new and not someone elses abused toy! John