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[Datsun 1200 encyclopedia]


From Datsun 1200 Club

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Categories: Fuel System | Hitachi 306 Carburetor

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.



The DCH306 carburetor is a very good carburetor. It only has 2 or 3 vacuum hoses on it.

1. Vacuum advance port
2. Choke Pull-off port & diaphragm
3. EGR port (added with 1974 North America models)

Additionally models which use the Throttle Opener system have the T.O. diaphragm attached to the carburetor which uses manifold vacuum. It has no carburetor vacuum connection.

California models eventually added 2 or 3 ports for Altitude Compensation. This added to the hose count. Technically they are not vacuum connections but are external connections to the air bleeds. A leaking hose here will lean the air-fuel mixture but under different conditions than a vacuum leak.

In 1981 one last hose was added, not a vaccum hose but a large diameter vent hose to the top of the fuel bowl.


Note that while new revisions to the DCH306 were introduced in some models, other models continued to use prior versions of the DCH306. This means the year of a DCH306 cannot be determined by the features alone.

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
1980: 3rd port for Altitude Compensator fitted with a pipe
 Certain models
1981: the "new" DCH306 - the DCR306 is introduced
* Vacuum-controlled Secondary Throttle actuator added
* Replaceable fuel bowl sight-glass added
* Vented fuel bowl incorporated

1972 Datsun 1200

The DCH306 was introduced for 1972 North America models in June 1971. Its only noticeable feature over the DCG306 was the addition of Automatic Choke. This is a fairly simple reliable system that it totally automatic.

DHC306 began with DCH306-1, for North America Datsun 1200 Manual Transmission.


For 1973 North American models, and Anti-diesel valve was added to prevent engine run-on. This required a new casting, but no other changes were made. Change occured July 1972 for the 1973 model year.

Anti-diesel started with DCH306-4.


A new casting was introduced with the North American models. The casting has an EGR vacuum signal port, and provision for an external Altitude Compensator.

EGR Port

An EGR port was added to the DCH306 for North American models. This port is slightly above and to the side of the vacuum advance port.

See main article: EGR

Altitude Compensator Ports

California models for 1975 introduced the Altitude Compensator. Some non-California models used the new casting, but holes are not drilled, so no leaks are possible in those models.

Same castings with and without the holes drilled:
23416.jpgAlbum 23416

See main article: Altitude Compensator


See main article: B210 Carburetor 1978


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

California models use the 3rd Altitude Compensator port on the carburetor to improve fuel economy by leaning the mixture at certain times. This occurs with the engine coolant is below 35F OR when 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

Although not requiring any special carburetor feature, 1980 saw the introduction of the Fuel Shut-Off System for increased economy. It cuts fuel flow while the engine is decelerating.

See main article: Fuel Shut-Off System

In 1980, only California models and the A15.MT models used the FSOS.


New carburetor from 1981 is similar to DCH306 but has vacuum secondaries.

See main article: DCR306


Feedback carburetor from 1989 Datsun 1200 is similar to DCR306 but has electronic mixture solenoid controlled by ECU.

See main article: DCZ306

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This page has been accessed 19,146 times. This page was last modified 08:05, 7 February 2017. Content is available under Datsun 1200 Club.