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.
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.
NOTE: Competition versions of flat-tops do not have IMS. They are simply the old style carbs with the new tops.
Datsun Competition (Nissan Competition) sold a open-vented, non-IMS, system:
Supplied with simple vent tubes. Production A12T vents the carburetors to the air cleaner.
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.
Thick hoses: Idle Mixture System (IMS)
IMS body with Mixture Screw
Idle mixture (IMS) is possible with the new flat-top Hitachi design.
- First of all, check the ignition timing and set it correctly
- Next, check the float levels. Nothing will work correctly if this is off
- Check oil damper level, and top off with 10W-30 if needed
- Loosen balance adjusting screw completely
- Set idle speed to 750 rpm by turning idle speed screw
- Clockwise: speed decreases
- Anti-clockwise: speed increase
- Synchronize the twin carbs by turning Balance screw
- Turn Mixture screw back and forth until best lean idle is achieved
- Reset idle speed to 750 rpm
- 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)
|Hitachi Twin Carb|
|Hitachi Twin Carb A12T|
|Unsorted Twin Carb Photos|
|A12GX Engine Photos|
|A12T Engine Photos (B210 Twin Carb)|
|A14T Engine Photos|
|A12GX Carburetor Part Numbers|
|A12T Carburetor Part Numbers|
|A14T Part Numbers|
|Hitachi Twin Carb Adjustment|