The control unit is attached to the
metering unit by four nuts. A follower (15), with a diaphragm seal set
in an annular groove around its periphery, projects through the leading face
of the unit. The rear end of the follower bears against the outer two of
three rollers (13) carried on the control links (12), whilst the third
roller, of smaller diameter, runs against the fuel cam (11).
The control links are pivoted at the top
where they are attached to the center of a spring-controlled rubber
diaphragm, the lower part of the control links are free.
Two springs (3) are positioned between the
diaphragm and three concentric calibration screws (4). The top of the
diaphragm and the calibration screws are in a chamber connected by a pipe to
The fuel cam (11) is secured by two screws
to a carrier (8) which is in contact with an external control screw (14).
The carrier is pivoted at point X, the pivot being extended through the rear
face of the metering unit. The excess fuel lever (5) is pivoted at the rear
face of the unit and has a cam face at the lower end which contacts the cam
Engine fuel demands, according to throttle openings and load, are
reflected in changes in inlet manifold depression. The change is sensed by
the spring-loaded diaphragm, which takes up a position balancing the loading
of the springs (3) against the depression in the chamber.
The control links are thus raised or lowered along the cam track allowing
the follower to move further in or out of the forward face of the unit and
so regulate the metering unit control stop.
To prevent the full hydraulic force of the control stop
from impinging on the control linkage, a balancing spring (2) is fitted on
the follower which results in only light pressure
between the follower and the rollers.
The control springs at the rear of the diaphragm are
chosen to suit the engine requirements. They are adjusted, during
calibration, by the manufacturer and the adjustment MUST NOT BE DISTURBED.
The fuel cam (11) is secured to the carrier by two screws
(C Fig. 16) the holes in the cam are slotted to enable the correct fuel
control slope to be set. An external adjusting screw, acting on the fuel cam
carrier, determines full load setting. The above adjustments MUST NOT BE
Movement of the excess fuel lever is
transmitted to the fuel cam and carrier which are pivoted at point X.
When the lever is turned, the fuel cam and carrier are moved against the
tension of the return spring, allowing the rollers, follower and control
stop to take up a position providing up to 300% extra fuel.
The injectors are fitted into the inlet manifolds and
upon their performance depends the correct atomization of the fuel. A poppet
valve in the injector is set to open at approximately 50 p.s.i. and give a
60 degree hollow cone spray.
In addition to normal service precautions, the following
are peculiar to petrol injection engines.
(a) Before subjecting
a vehicle to a lengthy overhaul or a prolonged period of idleness, a petrol
inhibitor should be added to the fuel and the engine run to ensure complete
circulation throughout the system. The gummy residue, from evaporated
petrol, is thus prevented from seizing the shuttle and other close-
tolerance parts in the system.
(b) The fuel pump
must not be switched on whilst any part of the pressurized circuit is
(c) The fuel pump
must not remain switched on for lengthy periods whilst the engine is
stationary. If the ignition circuit is required to be switched on without
running the engine for lengthy periods, disconnect the electrical
connections to the pump.
(d) Do not re-use
sealing rings, always use new ones.
(e) Subsequent to an
overhaul it will take some time to re-prime the fuel system, therefore,
crank with full choke until the engine starts. Do not attempt to re-prime
with a battery in a low state of charge.
Piping and Unions
Because of the comparative high pressures used on the
fuel system it is imperative that all union connections are securely
tightened and that the piping is regularly inspected for fretting, kinking
The rubber tubing used on the leak-off return pipe must
be carefully replaced to prevent kinking and ensure that the steel pipe does
not bite into the rubber and so block the pipe.
The leak-off pipe will, if blocked, cause a pressure
build up in the metering unit which will prevent full recuperation of the
follower and consequently allow excess fuel to be delivered, resulting in
sooting up of the plugs combined with uneven running.
Routine maintenance on the petrol injection system is restricted to
renewing the fuel filter every 12,000 miles as follows:
Lift the luggage compartment lid; turn back the carpet and remove the
left-hand section of the floor panel.
Slacken the nut securing the filter clip to the reservoir stud. To
prevent fuel leakage clamp the hoses on each side of the filter. Remove the
hoses from the filter.
Fit the new filter with the side marked IN connected to the
reservoir hose. Release the hose clamps, tighten securing clip.