s u Carburetor

8/22/2019 s u Carburetor

1/9

GOPAL GUPTA

RM3901B38


2/9

SU Carburetors were a brand ofcarburetor usually ofthe side draught type but downdraught variants wereused on some pre-war cars.

The unique S.U. (Skinners Union) Carburetor

provides precise control of both air flow and gasolineflow, according to the needs of the engine at thatmoment. An oil-damped Piston rises and fallsaccording to engine vacuum (throttle opening and

load).The Piston lowers or raises a fuel-metering Needle in

or out of a jet. At the same time, the bottom of thePiston varies the size of the carburetor throat opening.
http://en.wikipedia.org/wiki/Carburetterhttp://en.wikipedia.org/wiki/Carburetter


3/9

SU carburettors featured a variableventuri controlledby a piston. This piston has a tapered, conical meteringrod (usually referred to as a "needle") that fits insidean orifice ("jet") which admits fuel into the airstreampassing through the carburettor.

Since the needle is tapered, as it rises and falls it opensand closes the opening in the jet, regulating thepassage offuel, so the movement of the piston controlsthe amount of fuel delivered, depending on enginedemand.
http://en.wikipedia.org/wiki/Venturi_pumphttp://en.wikipedia.org/wiki/Pistonhttp://en.wikipedia.org/wiki/Cone_(geometry)http://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Gasolinehttp://en.wikipedia.org/wiki/Gasolinehttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Cone_(geometry)http://en.wikipedia.org/wiki/Pistonhttp://en.wikipedia.org/wiki/Venturi_pump


4/9

The flow of air through the venturi creates areduced static pressure in the venturi. This pressuredrop is communicated to the upper side of the piston

via an air passage.The underside of the piston is open to atmospheric

pressure. The difference in pressure between the twosides of the piston lifts the piston. Opposing this are

the weight of the piston and the force of a spring thatis compressed by the piston rising.

Because the spring is operating over a very small partof its possible range of extension, its force is

approximately constant. Under steady state conditionsthe upwards and downwards forces on the piston areequal and opposite, and the piston does not move.
http://en.wikipedia.org/wiki/Static_pressurehttp://en.wikipedia.org/wiki/Static_pressure


5/9


6/9

SU Carburetters were supplied in several throat sizes inboth Imperial (inch) and metric (millimeter)measurement. The carburetor identification is made byletter prefix which indicates the float type

"H": in which the float bowl has an arm cast into its base,which mounts to the bottom of the carburetor with ahollow bolt or banjo fitting. Fuel passes through the arminto the carburetor body. The bolt attaches to thecarburetor body just behind the main jet assembly.

"HD": the float bowl mounts with its arm fastening directlybelow, and concentric with, the main jet. The arm has a

flange that fastens with 4 screws to the bottom of thecarburetor, and sealed with a rubber diaphragm integralwith the main jet.


7/9

"HS": the float bowl is rigidly mounted to thecarburetor body, but fuel is transferred by a separate

external flexible line. "HIF": the float bowl is horizontal and integral (hence

the name).

The Imperial sizes include 1-1/8", 1-1/4", 1-1/2", 1-3/4", 1-

7/8", and 2", although not every type (H, HD, HS, HIF)was offered in every size.


8/9


9/9

THANKS

Documents

s u Carburetor