S.U. Carburetors

Octagon Newsletter January 2001

By Alan Fraser

Most stock MGs are equipped with S.U. carburetors. This fact gives rise to all sorts of disparaging remarks as, with the possible exception of body rust, they are blamed for most problems of ownership. In fact, the S.U. carburetor is a simple device which, if properly set up, will give years of trouble-free service. As a wise British mechanic once declared:

"The only thing wrong with the S.U. Carburetor is the Lucas wiring!" Many people do not even know what the initials stand for. Therefore let me bore you with some automotive history.

At the turn of the 20th Century there was a well-known British shoe company called Lilley and Skinner. In 1905, a member of the Skinner side of the partnership, George H. Skinner, was granted a patent on a carburetor. At this time, automotive carburetors were amazing contraptions that fed gasoline and air mixtures to engines via labyrinths of valves and pipes, all subject to changes in humidity, air pressure, octane, the phase of the moon and whether or not there were more than thirty days in the month. Mr. Skinner thought there must be a simpler way and, accordingly, patented the variable venturi carburetor with only one jet, a piston and a tapered needle.

He and his brother, Thomas Carlyle Skinner, produced a working model and named their business the "S.U. Company", the initials standing for "Skinners Union". They set up a small workshop on the premises of George Wailes and Co. in Euston Road, London, where all the machining for the early production runs was done. Based on their knowledge of the shoe business, they used leather in parts of their product. As their business increased, they moved to a larger facility on Prince of Wales Road, London. When World War I intervened, the firm began making machine gun parts.

Following the War, the general recession in the automotive business, forced the small company to make radio parts, windscreens, water cocks and other such products in order to survive. As the recession eased, the company turned once more to producing carburetors which were found on such quality autos as Bentley, Invicta and Napier.

Morris Motors purchased the S.U. Carburetor Co. in 1926. Mr. G. Skinner was named a Director and the operation was transferred to Birmingham alongside the Morris Commercial Cars Ltd. factory. The company rapidly expanded as part of the Morris Empire and added electric fuel pumps to its product line.

Morris Motors formed the S.U. Carburetor Co., Ltd., in 1936 after total acquisition. When World War II started, the company once more contributed to the effort, this time manufacturing carburetors for Hurricanes and Spitfires of the Battle of Britain fame. They also developed a fuel injection pump used on later Spitfires and P-51 Mustangs.

After the War, the company continued to flourish. In 1976, they became a division of Service and Parts for British Leyland called S.U./Butec. In the next re-organization, the firm lost its name and became Austin Rover Fuel Systems. It was saved from oblivion when Burlen Fuel Systems Ltd. purchased the logo and invested heavily in producing genuine parts for all S.U. carburetors up to the HIF model, to target the classic car market.

The S.U. Carburetor is so simple that it was misunderstood by North Americans who were brought up on Stromberg and Carter carburetors with their idle jets, mixture jets, accelerator pumps and mounting atop the engine rather than stuck on the side. Also, only hotrods had more than one carb and that needed a progressive linkage. S.U. Carbs were definitely something alien!

In actual fact, once an S.U. carb is overhauled and set up, it should be left alone for the next few years except for occasional adjustment for temperature, altitude or engine wear. When I was younger and more foolish and raced my MGA at Westwood, I used standard inch and a half carburetors and often had the tachometer pointing to "Made in England" but never felt any fuel starvation or lack of response at high revolutions.

If you are having problems with running your car, check everything else before you begin tinkering with the carburetors. Even with a badly tuned engine, the S.U. carburetors are quite forgiving. Even if the throttle shafts are badly worn, they will function, but make tuning the engine very difficult. Repairing the shafts and renewing seals and gaskets will give you years of trouble-free motoring. As it is stressed in the Club video, once S.U. carburetors have been rebuilt, they should be adjusted only during tune-ups and then only after all other parts of the mechanicals have been checked.

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