Thought I'd see how the head and manifold lined up. Was suprised to find a big step down into the head. The inlet ports in the head are up from standard small bore of 15/32" to 13/16" as supplied by Mr Calver. However the C-AHT770 single SU manifold from Minispares has ports of 13/8". Even the standard manifold ports are chamfered to 13/8".
Vizard talks about chamfering the head ports to make them slightly bigger than the manifold ports which helps to reintroduce puddling fuel into the air stream and says that a step in this direction causes virtually no loss in flow. The way mine are I'll have a few cc's of fuel hanging around at the step into the head and a loss of flow. Thass orl a bit strange.