Rover's Vikingship The HIF 44 Carburettors
Part one
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HIF 44e Carburettors

On this section of our website we will start with the HIF 44.
Here you see the parts of the HIF 44e

1.   HIF44E Carburettor
2.   Fuel Cut-off Solenoids
3.   Stepper motor
4.   Vacuum switch
5.   ECU
6.   Ignition coil
7.   sensor air temperature
8.   High engine temperature lamp
9.   Engine temperature sensor
10. Throttle Switch
11.  Engine temperature sensor


Automatic Enrichment Device

We will start with the automatic enrichment device. It is a rotary valve, '1', which receives fuel from the carburettor's fuel reservoir '2' and air via a vacuum unit '3'.
The rotary valve is turned by the stepper motor '4'. The stepper motor receives its information to turn from the ECU.

In this diagram, the rotary valve contains a sleeve '1' and a spindle '2', the spindle being turned by the stepper motor. Fuel enters the valve from below and air from above. The emulsified mixture passes through hole 'A' in the sleeve and 'B' in the spindle to the centre of the spindle and from there into the venturi.

To control the amount of air/fuel mixture entering, a V shaped groove is cut into the periphery of the spindle.
Turning movement of the stepper motor will vary the position of the V groove relative to the hole 'A' in the sleeve, and thus meter the amount of air and fuel entering the carburettor.


Vacuum Valve

This vacuum valve is a further refinement to ensure correct engine performance under varying load conditions during warm up.
It is connected to the air intake side of the rotary valve, and receives vacuum from the inlet manifold.

When manifold depression is high, such as at idle, vacuum will lift the diaphragm off its seat against spring pressure. Thus air can enter the rotary valve through channels 'X' and 'Y'.
A reduced vacuum during acceleration-will allow the spring to seat the diaphragm. Channel 'X' will be sealed, and a much reduced volume of air will enter through channel 'Y'. This gives the richer fuel mixture necessary for correct engine performance during low manifold depression conditions.

You will now understand the effect that faults on the vacuum valve may have to poor carburettor performance during warm up. For example, if the pipe to the rotary valve is loose or split, excessive air will enter the valve to give a weak mixture. This will probably be noticed as hesitation on acceleration during the warm up period.


Throttle Jack

Another device new to the HIF 44e is this throttle jack. It is fitted to enable a slower idle speed to be used to improve fuel economy.
It is moved out by this cam farrowed) which is driven by the stepper motor. So it operates in concert with the rotary enrichment valve.

As the cam pushes the throttle jack out, it moves the linkage to the carburettor butterfly and increases the idle speed. In fact for the first 40 of spindle rotation, only the throttle jack is actuated; thereafter the porting in the rotary valve becomes progressively larger and additional fuel/air mixture passes to the carburettor.

As we have said before, the stepper motor is controlled by the ECU. So if the engine speed drops below its correct idle speed, the ECU will tell the stepper motor to turn. This will cause the cam to push out the throttle jack and correct the idle speed automatically.


Fuel Cut-off Valve

Now the fuel cut-off valve. It is fitted to reduce the amount of fuel able to be drawn out of the carburettor during overrun and so improve fuel consumption. Let us see how it works.
In this diagram, air at atmospheric pressure enters the float chamber at the left through a fixed air bleed. The solenoid operated fuel cut-off valve, fitted in a separate passage way on the right also allows air to enter.

Under acceleration and cruise conditions the valve is in the position you see here. Atmospheric pressure above the fuel in the float chamber allows the fuel to be drawn out of the jet and into the venturi.
When the solenoid operates on overrun, the valve opens a passage to the venturi. Air is drawn from the float chamber and fuel flow is reduced.

The cut-off valve is told when to operate by the ECU. It receives a signal from a switch at the throttle pedal to say that the driver's foot is off. it also receives engine speed information to ensure it does not work below 1300 rpm.
Incidentally it does not work continuously during overrun. It opens and closes at 1/2 second intervals for a period of 9 seconds to make sure there is sufficient fuel available to avoid stalling, or hesitation when the driver accelerates again.


The HIF 44 Carburettors part two

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