Hitachi Twin Carb A12T

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A12T is the twin carb engine fitted to Datsun Sunny B210 and Nissan Cherry PE10. It uses the Hitachi Twin Carb system, dual 38mm Hitachi sidedrafts. These mainly differ from the A12GX Engine Hitachis in that they are have a new idle speed and idle mixture system. They can be easily distinguished by their flat tops.

Hitachi Twin Carb Twin Carb Overview A12GX Engine : A12T (B210) : A14T Hitachi Twin Carb Adjustment/Tuning Engine Photos A12GX : A12T : A14T : Unsorted Carburetor Part Numbers A12GX parts : A12T parts : A14T parts

Overview

JDM 1973-1975 B210 GX models had either an A12S (single-carb) or optional A12T (twin-carb) engine. While the A12T is very similar to the A12 GX Engine, it used different flattop Hitachis and a slightly different intake manifold with a few more fittings. These are good carburetors that are not jetted leaner, but instead have a closed fuel bowl vent system. They are almost identical to the dome-top carburetors except for the IMS fittings on the top of the carbs. They total system (inlet manifold and hoses) is more complicated to allow idle mixture and speed adjustments and capture all the gasoline fumes into the air cleaner.

JDM Datsun Cherry (E10) models also used the A12T engine, including the famous Cherry X1-R vehicle.

Idle Mixture System

Ummm... smells good, and works good too. JDM non-competition (stock) Hitachi sidedraft flat-top carburetors come with an advanced Idle Mixture System (IMS), for fine tuning of the idle mixture.

Album: Thick hoses are for Idle Mixture System (IMS)

Album: Idle Mixture System

Adjustments

Idle mixture (IMS) is possible with the new flat-top Hitachi design.

1. First of all, check the ignition timing and set it correctly
2. Next, check the float levels. Nothing will work correctly if this is off
3. Check oil damper level, and top off with 10W-30 if needed
4. Loosen balance adjusting screw completely
5. Set idle speed to 750 rpm by turning idle speed screw
   • Clockwise: speed decreases
   • Anti-clockwise: speed increase
6. Synchronize the twin carbs by turning Balance screw
7. Turn Mixture screw back and forth until best lean idle is achieved
8. Reset idle speed to 750 rpm
9. Lean out Mixture until speed drops to 725 rpm

Green: Hoses to air cleaner (including the curved IMS hose)

Blue: Fuel lines to fuel bowls

Red: Idle speed system (air bypass system), connects to IMS body vents

Blue: Fuel bowl vent lines

Green: IMS inner vent line (to Air Cleaner)

Red: IMS (Idle Mixture)

Competition Flat-Tops

Datsun Competition (Nissan Competition) sold a open-vented, non-IMS, twin carb system.

See main article: Competition Carburetors

NOTE: Competition versions of flat-tops do not have IMS. They are simply the old style carbs with the new tops. Similar or the same to the Datsun 810 SSS twin carbs (200B or Euro 810 carbs).