How to Check and adjusting the choke operation on an SU carburettor

Checking and adjusting the choke operation on an SU carburettor.

The choke on an SU carburettor is operated by a cable that draws down the jet to increase the flow of fuel through the carburettor. As the jet is drawn down, so a fast-idle cam opens the throttle valve slightly to produce a fast idle.
Operate the choke control knob and check that the jet drops down and returns fully when the choke knob is released.

Lubricate the Jet lever Pivot point where it is fixed to the jet, with light machine oil.
Disconnect the choke inner cable from its clamp in the choke lever, and reconnect it with in 1/16 inch (1.5875 mm). free play. Pull out the choke knob until the choke lever just starts to move the jet.

Start the engine and run it until it reaches operating temperature. Adjust the fast-idle screw to give a speed of approximately 1000 rpm, or a
fast-idle speed.
When the choke is operated on cold starting, this will open the throttle valve sufficiently to give a fast idle.