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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. | 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 | + | = 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. | + | 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. | ||
1972: Debut with automatic choke | 1972: Debut with automatic choke | ||
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1981: Vacuum-controlled Secondary Throttle actuator added | 1981: Vacuum-controlled Secondary Throttle actuator added | ||
1981: Replaceable fuel bowl sight-glass added | 1981: Replaceable fuel bowl sight-glass added | ||
+ | 1981: Vented fuel bowl incorporated | ||
= 1981 = | = 1981 = | ||
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== 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. | + | 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 == | == 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. | + | Although not requiring any special carburetor feature, 1981 saw the introduction of the Fuel Shut-Off System for increased economy. It cuts fuel flow while the engine is decelerating. |
- | FSOS was used by CAL, FED, FED.MPG and FED.CAN models. Canada models did not use fuel-shut off except for MPG models. | + | See main article: [[Fuel Shut-Off System]] |
Revision as of 12:13, 13 January 2012
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.
Contents |
Overview
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.
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: Vented fuel bowl incorporated
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
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, 1981 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