[OG68]

Both snorkels are normally open with engine off.
With engine running and vacuum applied, both snorkels should close. The drivers side is then controlled by the thermo switch to open as the temperature increases, gradually restricting vacuum as the temperature rises.
The passenger side will remain closed until the throttle is wide open and vacuum drops to zero. It will then open allowing more air to the carburetor. It will remain closed during normal cruising and idle conditions. .

The vacuum hose ‘T’ is between the manifold and temperature switch. Only the drivers side is controlled by the switch.