Finally after much head scratching and replacing of parts the 750 Commando is running sweet as a nut now. Issues I found were that first the head gasket was blown, one of the head nuts was missing, the Boyer ignition despite being new seemed to not be working properly and both main and reserve petrol taps were effectively blocked up. So New rings and gaskets, new Pazon Ignition (quality bit of kit!) New 34mm Mikuni carb and some good functioning petrol taps and it runs great. This thing has done less than 9000 miles from new and is the nearest thing to a new Commando I've worked on (despite being 37 years old... the bike that is, not me! ) For a while this bike had beaten me but not now, another Norton tamed!!