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Some Datsuns were fitted with sidedraft carburetors right from the factory. Usually fitted with twin Hitachi variable venturi carburetors which are very similar to S.U. (Skinners Union) carburettors from Britain. The Datsun 1200 GX models were fitted with twin Hitachi 38mm carburetors. Many Datsun fans refer to the Hitachis as "SUs", so keep that in mind when you read information. It may be about the Hitachi sidedrafts, or it may not.

Reportedly, Hitachi licensed the SU design, but I have yet to see a reference for that (Nissan manual, etc).

Datsun twin-carb setups used two basic Hitachi sizes:

38 mm (1-1/2 inch bore) on most cars
46 mm (1-7/8 inch bore) on Z-cars. These are too big for Nissan A engines (even if you use one) and reportedly the late model flat top 46s are a bad design.

For true bolt on experience, you will need a complete setup:

Intake manifold
Exhaust manifold (twin down-pipe cast headers). The clearance differently than regular manifolds
Two carbs
Fuel lines
Accelerator cable & linkage
Choke cables
Air cleaners

In general on a given manifold you can use SU, Zenith-Stromberg (ZS) or Hitachi sidedrafts, but note that the linkage, hose locations and air cleaner attachment will vary.

1 Three Different Designs
2 Parts Donors
3 Tuning
4 Troubleshooting
5 References
6 Parts Suppliers
7 Links
8 Photo Index

Three Different Designs

A12 GX Engine

(The Datsun 1200 GX Engine)
B110 GX (Grand Luxe Twin-carb) models were fitted with the A12 GX Engine. This featured a matched pair of left- and right- hand Hitachi HJE38W sidedraft carbs. These mount at an angle and feed into the monster GX ports of the cylinder head. On a RHD car there is clearance aplenty, but on a LHD car fitting an air cleaner it a bit tricky. But this is more easily fitted to LHD than a twin-Weber setup.

These are the true "dome-top" Hitachis, already setup for performance. They can use standard SU needles so tuning it quite easy.

Choke Linkage

The A12GX used a twin-cable Choke knob. However, you can use the stock single cable with a simple bracket on the carbs to operate both:

A12T Engine

(The B210 Engine GX-T Engine)
Some Cherry models, and 1974-1975 B210s had the A12T twin-carb engine. While very similar to the A12 GX Engine, the A12T engine used different, flattop Hitachis and a slightly different intake manifold.

A14T Engine

(B210 GX-T Engine)
Starting around 1976, the A12T was phased out and the A14T started. Unlike the original A12GX engine with its monster intake ports, the A14T used standard A14 oval ports (28 x 34 mm).

These are flat-top carbs, probably the same as L18SSS engines, heavily modified from the original SU-style design, apparently to add much emission controls. These are decent carburetors that only need a few simple modifications.

LOOK! A14T manifold photo gallery

Features:

EGR port
Flat-top triangular-bell Hitachis
Vacuum ports on each end, top of manifold
No PCV valve fitting

Carb side:

4-bolt pattern on 3.5 in. circle
1.5 inch bore
Carb spacing approx 7-1/8 inch
Water ports at bottom

Parts Donors

A12 GX import engines
Datsun Competition setups
Datsun Roadsters: Reportedly, all Roadsters were fitted with Hitachis except the 2000 Roadster (2-liter engine) which came with Solex carbs.
Datsun 411 SSS (circa 1966)
Datsun 510 SSS
Datsun 610/710 SSS

Tuning

Go here for lots of information: The Hitachi-SU Tech Pages.

Troubleshooting

Go here for lots of information: The Hitachi-SU Tech Pages - Troubleshooting.

References

Nissan Motorsports catalog (#99996-CAT98 and other years)
Nissan Schematic catalog (#99996-M8015)

Parts Suppliers

Z-Therapy sells parts and complete setups http://www.ztherapy.com
Get the 510 SSS carb setup. The jetting is slightly different but otherwise they are the same
craigslist and other local sources (from time to time)
eBay from time to time

The parts although not common, are not rare in USA. Quite a few twin setups were found on import engines in the 1980s, and quite a few were purchased from Datsun Competition, so they can be found.

ZTherapy is in the USA, and always has them on hand.