Emission-control models are titled CDSE and CD2SE. Most of these allow no
or needle adjustment. The idle-speed screw is adjustable; there is also a 'trimmer' screw for minor adjustments to
flow, which may have a locknut.
Even this screw should be adjusted only with gas analysing equipment at a garage. On a few CDSEs the needle height can be adjusted with a special tool in the same way as on a CD3 (See ).
The jet-height adjustment may be made tamper-proof by replacing the adjusting screw with a bush, which needs a special tool to turn. The adjuster may also be covered by a steel cap. Adjustment is as for a normal Stromberg (See
Adjusting a Stromberg carburettor
Adjusting an SU type HIF
The earliest emission-control types of SU
were 'sealed' by no more than a dab of paint on the threads of the adjusting screws.
On later types, plastic
were fitted around the idling-speed and jet adjusters. These shrouds pull off easily, but cannot be put back.
The HIF model (which differs from other SU models by having a
chamber under the carburettor body, not beside it) has a screw in the side of the body to adjust the jet height.
This screw is hidden under an
plug which can be removed with a thin screwdriver.
The screw turns in,
, to enrich the mixture, and out to weaken the mixture.
There may also be an aluminium plug over the idle-speed screw rather than a plastic shroud. (For normal SU adjustment, see
Adjusting an SU carburettor
Adjusting a fixed-jet
The simplest type of seal used is a cap over the volume screw, often easy to remove. The screw, once uncovered, adjusts as normal (See
Adjusting a fixed-jet carburettor
). Sometimes a special screw head, requiring a matching tool, is used.
The system in widest use is to seal both the volume screw and the throttle-stop screw which controls the idling speed. However, there is an extra screw which alters idling speed by regulating air flow.
This 'by-pass idle-speed' screw is the only one which should be adjusted, and is usually the only screw which can be reached without removing a seal.
If not, it is normally larger than the fuel-volume screw and mounted higher up, either protruding or in a recess.
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resembles the simpler variable-jet type (See
How variable-jet carburettors work
) in having a
- a constricted neck - through which air flows on its way to the