TECHNICAL EXAMINING AN AUTOMATIC CHOKE
The general aim of a choke is to provide more fuel to the engine when starting it from cold. The extra fuel not only helps to ensure the engine remains running, but it can also move the vehicle. However, once the engine has warmed up, it doesn't need quite so much fuel to keep going, and excessive fuel can mean it runs too rich, fouling the spark plugs and washing the cylinder bores.
Traditionally, some means of manually altering the richness of the fuel was used to help with cold starting the engine. The manual choke was the initial answer and was still in use on many vehicles throughout the Eighties, such as the Austin Mini. However, many vehicles had adopted an automatic choke several decades before, including Jaguar.
The early design of automatic choke we're looking at was adopted by Jaguar during the late Forties and was called the auxiliary starting carburettor.
With most Jaguar XK engines being equipped with twin SU carburettors,initially part of the float chamber on the rearmost carburettor of the XK120, for example, but on later models, it was part of the frontmost carburettor.
