THE AUSTIN SEVEN CARBURETTOR
1936 - 1939
From the Austin Magazine
The Austin Seven has a Zenith horizontal type
carburetter. Petrol from the pump passes through the union, the filter and
the needle seating into the float chamber. As the float rises it will close the
needle on its seating, thus regulating the flow of fuel.
The
float chamber contains the main jet, the compensating jet, the capacity well and
the slow running jet. Petrol flows through the main and compensating jets and
rises in the capacity well. From the jets it flows along two separate channels
into a common channel in the emulsion block attached to the float chamber. This
main channel has its outlet in a nozzle which projects into the choke tube.
Atmosphere and the main channel of the emulsion block are in direct contact with
the capacity well.
Adjustments
Only necessary adjustments should be made and only then when the
engine has reached its running temperature.
If the engine does not idle as slowly as desired, turn the stop screw to the
left to close the throttle slightly. A weak mixture may also affect slow
running. This can be remedied by turning the air regulating screw in a clockwise
direction to enrich the mixture. However, do not make the mixture too rich or
the engine will “hunt” or tend to choke when the engine is slow running and
warm.
Controls
From time to time it is advisable to ensure that the choke and throttle
controls are operating freely— the strangler flap must open and close fully, and
the throttle control must return fully against its stop in the idling position.
Jet Settings
|
JET
|
SEVEN
|
BIG SEVEN
|
TEN
|
TWELVE
|
|
choke
|
17
|
23
|
23
|
25
|
|
Main jet
|
57
|
90
|
95
|
105
|
|
Compensating jet
|
50
|
50
|
50
|
60
|
|
Slow running jet
|
60
|
60
|
60
|
55
|
|
Progression jet
|
50
|
-
|
60
|
100
|
|
Needle seating
|
1.5mm
|
1.5mm
|
1.5mm
|
1.5mm
|
|
Capacity tube
|
2
|
-
|
2
|
2
|
These have been fixed after considerable experiment to ensure good fuel
consumption combined with good performance. They should not be changed other
than to replace old or worn jets unless it is desired to change the performance
and fuel consumption of the car.
Zenith jets sizes normally run in 5s, the higher the number the larger the jet.
Although settings may differ according to the special requirements of certain
markets, the standard jet sizes for Austin cars are as shown in table below.
Cleaning
The bowl of the carburetter should be removed occasionally for
cleaning. Take out two slotted retaining bolts and the bowl will drop into the
hand. On Sevens, Big Sevens, Tens, Twelves and Fourteens the float will fall out
when the bowl is turned upside down, revealing the main and compensating jets in
the bottom of the bowl. Care must be taken that float is not damaged. If dented
or punctured, a new float must be fitted. Remove the jets using the squared end
of one retaining bolt and a spanner or screwdriver. Note that on the
Eighteens, Twenties and Twenty-eights the jet cover must be removed before the
jet itself can be unscrewed.