Angus553

Hi Drawfiler  yes have checked all your suggestions as replaced o rings and the pump diaphragm(what a pain to get the spring to sit properly) the carbs are balanced and set to 3.5 full turns. After the last set up they were set at just over 4 turns and reading around 4 on the synchronometer. 
It seems the new electronic ignition had an intermittent fault as couldnt think of anything else. Swapped over 20+ plugs 3 dizzy caps 4 rotor arms and trigger wheels 2 ht lead sets and 2 coils and still got the same problem even with spark via cranking. New dizzy cap didnt help until the new electronic ignition arrived via a phone call to accuspark who were happy to replace it as was only 2 months old. 
Everything thus far seems to work with all the combinations just about and the position of the rotor arm and trigger wheel seem to be less critical now. the ignition switch and erretic rpm gauge also now seem to be ok again.
Just need to retune the carbs as played with them but do work ok anyway.

Oh dear....guess what, better scrap the above as have eventually diagnosed the problem and its location. The problem is a perished hose joining with the brass pipe connected to the carb.  So new hose required and the problem is no more  for now. Just have to put everything back together again.