[Gaz64]

Rune,

The can I've mentioned has advance and retard with two ports.
The advance plate would be at static timing with no vacuum applied.
The plate would move in either direction ( advance or retard ) depending on which port had vacuum applied to it.
Some have used this can for turbo applications with advance for off boost and retard under boost using just the advance port.

Swap your carbs around and prove your fault to one of them before condemning inlet manifold or an engine fault.