DCH306

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Hitachi DCH306 was first used in the 1972 Datsun 1200 for North America. It is just like the original 1200 carburetor DCHG306, but the H version has an Automatic Choke. This series continued to be modified, with an anti-diesel valve added for 1973 and was futher developed well into the 1980s.

= Overview The DCH306 carburetor is a very good carburetor. It only has 3 or 4 vacuum hoses on it. California models eventually added ports for Altitute Compensation.

1972: Debut with automatic choke
1973: Anti-diesel valve added
1974: EGR port added
1975: 2 ports for an external Altitude Compensator added
 California models only
1981: 3rd port for Altitude Compensator fitted with a pipe
1981: Vacuum-controlled Secondary Throttle actuator added
1981: Replaceable fuel bowl sight-glass added

1981

New type sight-glass introduced. This type is replaceable unlike previous versions.

Fuel bowl is now externally vented. This goes to a special 5-hose Charcoal Canister. The canister has a Vent Switching Valve which is open when the engine is not running, so that vapors from the fuel bowl can go directly to the charcoall filter. When the engine starts, vacuum from the intake manifold closes the VSV.

Altitude Compensator ports marked 1,2,3

Vacuum-Secondary introduced

3rd A-C Port

California models: 3rd port for Altitude Compensator is finally fitted with a pipe.

See main article: Altitude Compensator

This port is also used for the Mixture Ratio Rich-Lean Exchange System.

Mixture Ratio Rich-Lean Exchange System

The 3rd Altitude Compensator port on the carburetor is also used to improve fuel economy by leaning the mixture at certain times. This occurs with the engine coolant is below 35F OR when the it is above 35F and above 40mph. This only leans the Primary-side of the carburetor via the main air bleed port. At high altitudes the Altitude Compensator opens this line, so the MRRLES has no effect at high altitudes.

Fuel Shut-Off System

Fuel Shut-Off System introduced in 1981 leverages the anti-diesel valve to stop the fuel flow to the slow-speed system during periods of deceleration. This is similar to what EFI systems do.

FSOS was used by CAL, FED, FED.MPG and FED.CAN models. Canada models did not use fuel-shut off except for MPG models.