Altitude Compensator

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Hitachi DCG-306 V-spec carburetors starting with 1976 B210 California models employed an Altitude Compensator mechanism. So the car runs in tune both at sea level and at high elevations -- and everywhere in between.

Overview

The Altitude Compensator is a totally automatic operation. It works by the bellows moving per altititude, exposing more or less air to the air bleeds inside the carburetor.

Diagram from the 1981 B310 Factory Service Manual

Same castings with and without the holes drilled:

Early

Hitachi with 2-hose compensator.

Late

Hitachi with vacuum secondary and 3-hose compensator.