Altitude Compensator

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Hitachi DCH-306 V-spec carburetors starting with 1976 B210 California models employ 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 three types different years:

• Bellows
• sensor similar in looks to the A.T.C. and idle compensators
• manual switch

Same castings with and without the holes drilled:

1976

It uses a bellows.

FSM refers to it as an installable option:

• Drill hole in bottom of air cleaner, insert fitting
• Run hose over the to Bellows. Mount that on the side of the coil/electronics cover (on strut tower)
• Run two small hoses from Bellows to Carburetor
• Set idle speed and mixture

Hitachi with 2-hose compensator.

1977-1978

California (V) models use a carburetor with two fittings which lead to the air jets. A valve in the air cleaner connects to those via hoses. The valve is manually configurable to either H or L position.

Counties in USA 1,219m (4,000 ft) or more above sea high have been designated "High Altitude Counties" (see 1977 B210 Service Bulletin).

• At low altitudes: closed
• At high altitudes: open

Remember to move the switch when you get to a legally-designated HAC -- and then readjust the mixture and idle speed. This is not an automatic system.

1979

Apparently 1979 models did not use a compensator.

1980

Bellows system like 1976 adopted. On above 600 m (1,978 ft). Non-adjustable.

1981-1982

1981 used an Altitude Compensator with totally automatic operation. It works by a bellows moving per altitude, exposing more or less air to the air bleeds inside the carburetor.

• Operates above 500 m (1641 ft)
• Adds a third hose, for primary slow air bleed
  • 4-fitting bellows
  • 3-fittng carburetor

Diagram from the 1981 B310 Factory Service Manual

Hitachi with vacuum secondary and 3-hose compensator.