Est. 1904

The Story of SU Carburettors

From a North London workshop to the engines of Spitfires and Jaguars — the remarkable journey of the world's finest carburettor.

Two Brothers and a Better Carburettor

The story of SU begins with two brothers: George Herbert Skinner (known as Bert) and Thomas Carlyle Skinner (known as Carl). Herbert was a pioneering motorist who grew fascinated by the internal combustion engine at the turn of the twentieth century. Frustrated by the crude fuel delivery systems of the day, he set about designing something fundamentally better.

In 1904, after years of experimentation, Herbert built the first Union Carburettor. His wife reportedly sewed the first leather bellows by hand. That original prototype was later donated to the Science Museum in South Kensington, where it remains today.

Herbert filed for a patent in 1905, granted in early 1906. Carl, who had worked with the Farman Automobile Company in London, joined his brother in commercialising the invention. In August 1910, S.U. Company Limited — Skinner's Union — was formally incorporated, and manufacture began at a factory on Prince of Wales Road in Kentish Town, North London.

The Genius Behind the Design

What made the SU fundamentally different was its constant-depression principle. A conventional fixed-jet carburettor requires a maze of jets, accelerator pumps and choke devices to deliver an acceptable mixture across engine loads. The SU did away with all of that.

A sliding piston rises and falls in response to the pressure drop created by airflow. Attached to this piston is a tapered needle sitting inside a single jet. As the piston rises, the needle lifts — widening the fuel passage in precise proportion to air demand. A dashpot filled with light oil dampens the piston's movement, acting as an accelerator enrichment system whenever the throttle is opened sharply.

The SU achieved with one jet and one needle what rivals needed dozens of components to approximate. That simplicity explains why it became the carburettor of choice for virtually every serious British manufacturer, and why it is still in production today.

Morris, Birmingham and a New Chapter

Despite the carburettor's technical merits, early sales were slow. The First World War diverted the factory to machine gun parts. After the Armistice, the Skinners struggled to build commercial momentum. Carl's solution was bold: he approached William Richard Morris — the Oxford car manufacturer who would become Lord Nuffield — and sold him the business.

Morris moved production to the Wolseley factory at Adderley Park in Birmingham, integrating SU carburettors across his growing vehicle range. Carl Skinner remained as Managing Director until his retirement in 1948. In 1936, S.U. was transferred into Morris Motors, and later became part of the British Motor Corporation, and ultimately British Leyland.

Powering Britain's Finest Cars

Through the 1930s, 1940s and beyond, the SU became the defining carburettor of British motoring. MG, Jaguar, Triumph, Austin-Healey, Rover, Aston Martin, Rolls-Royce, Bentley and Riley all fitted SUs. The carburettor's self-adjusting nature made it the natural choice for performance applications where a fixed-jet design simply couldn't keep pace with a driver's demands.

The HS series, introduced in 1958, became the definitive SU — fitted to everything from the Morris Minor to the twin-carburettor setup of the MGB. The later HIF (Horizontal Integral Float) design of 1972 modernised the layout for the tighter engine bays of the era.

Even Volvo, Datsun and motorcycle manufacturers recognised the SU's advantages. Hitachi built SU-licensed carburettors for the Datsun Z-series sports cars. Harley-Davidson owners retrofitted SUs for superior altitude compensation. The constant-depression principle was so effective it was widely copied — by Stromberg, Keihin and Ford's variable-venturi design — though none matched the elegance of the original.

Above the Clouds: SU at War

The most dramatic chapter in SU's history unfolded in the skies above Britain. During the Second World War, the Rolls-Royce Merlin — which powered both the Spitfire and Hurricane — was fitted with SU dual-choke updraught carburettors. These were excellent devices for level flight, but harboured a critical vulnerability.

When a pilot pushed into a steep dive, the resulting negative G-force caused fuel to flood the top of the carburettor's float chamber rather than flow into the engine. The engine cut out — precisely when maximum power was needed. German fighters used direct fuel injection and had no such problem; they learned to evade pursuing RAF aircraft simply by bunting into a dive.

The solution came from Beatrice "Tilly" Shilling, an aeronautical engineer at Farnborough and accomplished motorcycle racer who held a Brooklands Gold Star for lapping at over 100mph. In early 1941, Shilling devised a small brass restrictor disc — a precisely dimensioned washer fitted into the fuel line — that solved the flooding problem without taking aircraft out of service.

Shilling and her team toured RAF bases, fitting the devices to front-line aircraft. By March 1941, the modification — affectionately nicknamed "Miss Shilling's Orifice" by the pilots — had been installed throughout Fighter Command. It was a stopgap, but it worked, and it changed the balance of the air war at a critical moment.

Burlen and the Modern Era

By the early 1990s, fuel injection had displaced the carburettor on new cars. The S.U. Carburetter Company was voluntarily wound up in December 1994 — seemingly ending a ninety-year story.

But the demand from classic car owners never disappeared. In 1996, Burlen Fuel Systems of Salisbury acquired the SU name, intellectual property and manufacturing rights. Rather than consigning SU to history, Burlen invested in the tooling and expertise needed to keep genuine carburettors and fuel pumps in production. Today, every SU part sold through SU Specialists is manufactured to the original Burlen specification — the only company authorised to produce genuine SU components.

From the HS2 on a Morris Minor to the HD8 on a Jaguar E-Type, the same engineering philosophy Herbert Skinner developed in North London in 1904 continues to keep Britain's classic cars on the road — more than 120 years later.

SU Carburettor Types at a Glance

Type	Introduced	Key Feature	Common Fitments
H	1937	Float bowl arm cast into base	Pre-war and early post-war British cars
HD	1954	Float bowl concentric with main jet	Jaguar XK/E-Type, large Austin-Healey
HS	1958	Rubber-mounted float bowl, external pipe	MGB, Morris Minor, Triumph TR series, Sprite/Midget
HIF	1972	Horizontal integral float bowl	Later MGB, Triumph, Mini