I think i have discovered why my 1275cc engine will not idle cleanly and proving difficult to set mixture,idle and balance.As I understand it the inlets are siamesed 1/2 3/4 and have a carburettor shared across the 2 cylinders.Therefore no mixture transfer should exist between the two intakes.If you look at the library pic of the manifold,the large nut in the centre covers a hole which exposes an airway about 1/4" between the the two inlets.On my manifold this bolt is bareley long enough to catch the recessed threads and doesnt have anything to block down and seal this transfer airway.Like most old cars it is probably full of bits that are wrong.Comments as to whether I am on the right track or not.

This is normal to have a link pipe between the two inlet tracts. Un even idling on a twin carbed A series is usualy down to carbs that are in a bad state of repair. Usualy air leaks. Remove the 3 throttle return springs and check for 'play' in the two brass buttery fly shafts that go through the carbs. This is usually the culprit, if theres any more than a very slight amount then this will be your problem. Following this, also check oil level in the dash pot's - put in something like 5w/30 for good damping. Its also worth checking the carb balance with a carb balancer (a good one is ~£50).