Rover's Vikingship The F.A.S.D. Control
Rover's Vikingship


This part of site is an attempt to organize and add to the web resources for the Rover SD1 to form a cohesive and easily usable guide for those of us without easy access to expert repair and/or advice. It is not offered in any way as a definitive source and we take no responsibility for any errors that may exist.
Webmaster Rene Winters.


In this section, we will examine the Zenith Fully Automatic Starting Device F.A.S.D. fitted to the Rover SD1.
The FASD is controlled by coolant temperature. Coolant passes through the FASD (on the right), and air enters at the top from the air cleaner. Fuel is supplied from the carburettor float chamber.
Here we have removed the blue cover to see more of the mechanism. Inside the water jacket '1' is a wax capsule, which expands against a spring inside tube '2' as coolant temperature increases. This expansion pivots the drive lever '3' which in turn pushes down the metering needle '4' and shut-off valve '5'. The air valve '6' is located in the air intake.

In cross section, you can see the metering needle '4', the shut off valve '5' and the air valve '6'. In the static position, the air valve is held closed by two springs '7' and '8'. The area around the lower spring '8' is connected to manifold depression via a delay valve '9'. The delay valve contains a bimetal strip '10' which in its rest position holds a ball '11' on its seat.
During cranking, the air valve is held closed and fuel is drawn past the needle valve into the outlet '12' to the engine.
As soon as the engine starts, current passes to the bimetal strip '10' in the delay valve. The strip bends to allow the ball off its seat, and this in turn allows vacuum into the area around the lower spring '8'. This vacuum acts down against the force of the spring, and the air valve will open to weaken the mixture.
From there on, the warming coolant heats the wax capsule to move the linkage and progressively push down the needle and shut-off valve. When the engine is fully warmed up, the needle and valve are closed and the engine runs on the carburettor only.

Next the accelerator pump. It is necessary for the FASD to provide additional mixture during acceleration. The pump is located in the base of the FASD, and the plunger to it (arrowed), is moved down by the linkage from the wax capsule.

In this diagrammatic cross-section, you can see the components of the pump. The spring loaded vacuum valve '2', links manifold depression '1' to the chamber '3'. The chamber is split by a diaphragm '4', held down by a spring '5' and under which is fuel supplied via inlet valve '6'.
It works like this. During high manifold depression conditions (seen on the left), the diaphragm is raised against spring pressure. This draws in fuel under the diaphragm. When the throttle is opened, (on the right), depression above the diaphragm decreases, allowing the spring to push it down. Fuel is discharged through the exhaust valve to richen the mixture.
The items highlighted here cause the amount of fuel pumped to be progressively reduced as the engine warms up. This control is achieved by the drive lever '7' which as we saw earlier, is moved by the linkage from the wax capsule. As the engine warms up, the drive lever will push down the plunger '8'. This restricts the upward movement of the diaphragm and reduces the fuel delivery.

We have already mentioned the electrically controlled delay valve, so before we move onto FASD checks and adjustments a word about the electrical circuit.

As we said before the delay valve '1' is a bimetal strip which holds a ball on its seat when cold. It is connected to its control module '2' which is located behind the instrument panel. The control module receives information from the coil '3' and the ignition switch '4'.
When the engine starts, as soon as 200 rpm is reached, current passes to the delay valve. The bimetal strip then heats up to unseat the ball and allow vacuum under the air valve. The current draw is 5 amps initially, dropping to 0.5 - 0.7 amps to hold the valve open.


Now testing the FASD. Check the tightness of all the hoses; always make sure there is fuel being delivered and that coolant flows round the Wax capsule.
If the engine will not start from cold, check that the outlet pipe into the inlet manifold is wet with fuel. If it is dry check the fuel supply then suspect a faulty FASD.
It may also be caused by a fault in the electrical circuit to the delay valve.

First check the voltage by connecting a voltmeter between the delay valve input terminal and earth. During cranking there should be a zero reading, but as soon as the engine starts, it should increase to battery voltage, 11-13V.
You must also check the current flowing. The amperage during starting is 5 amps, but approximately 25 seconds after the engine has fired, it will drop to 0.5 - 0.7 amps as you see here.
If the engine starts but runs rich when hot, you should suspect a faulty FASD unit. To check, make sure the engine is at running temperature, connect a CO meter, and note the reading.
Disconnect and blank the manifold intake from the FASD unit, then note the CO reading again. If it rises slightly, this is acceptable and the FASD unit is OK.
If the CO reading drops significantly, then the FASD unit is sticking open and should be changed.


There is one adjustment that can be made to the FASD, but this should only be done after all other checks have been carried out. It involves altering the tension on the spring opposing wax capsule expansion, thus changing the temperature at which the FASD operates.
To do it you will need a 1.5mm Allen key and a special test kit from Solex.
Starting with a cold engine, degrease the wax capsule water jacket and attach a temperature sensitive label from the test kit.
Start the engine and allow it to idle, then position an 'air shut-off' indicator over the FASD intake so it is held in place by vacuum.
Fit the Allen key in the end of the spring location and watch the temperature sensitive label very closely as the engine warms up. Its segments will progressively change colour from grey to black, and as soon as the 65 square starts to turn black, turn the allen key clockwise until the air shut-off indicator falls off.
That completes the adjustment, but you must do it within 30 seconds. If you do not, you will have to wait for at least one hour for the engine to cool, then start again using a new temperature sensitive label.

Identification of the F.A.S.D. Units

Isolated cases have been reported of incorrect FASD units being fitted in Service, whilst they are identical externally, the vent fitted to each model differs internally. They can be identified by a reference number stamped under the body casting on the side furthest from the carburettor immediately below the blue plastic cover.
Specifications are as follows:
Vehicle Type         FASD Ref No.       BL Part No.
Rover 2000               4130                TZX 1005
Rover 2300               4132                TZX 1007
Rover 2600               4131                TZX 1006
Rover 3500               4027               AEU 2456

F.A.S.D. Manuel Kit
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© RWP sept. 2003