OPERATION OF THE FINAL FUEL INJECTION SYSTEM

Lever (3) is linked to the throttle plate shaft (8), and pivots about (7), the position of which is adjustable by means of the cockpit mixture control. Throttle movement is followed by the injector plunger (4), in accordance with the shape of cam (1).

Fuel pressure to the injector is governed by diaphragm (12). An increase in airflow through venturi (6) develops a vacuum under diaphragm (12) to add pressure on the relief valve(14), so as to cause an increase in the fuel pressure delivered to nozzle (5).

Fuel pressure at idle, i.e. when there is near zero vacuum, is set by adjuster (11), which varies the spring loading on valve (14). Coarse screw thread (20), fixed to the end of the cockpit mixture control shaft (22), is connected by the link (21), to the lever plate (19), which pivots about (18), to move the pivot (7), of lever (3). (Underneath and not fully visible in the photo.)

Throttle plate shaft (8), is fitted with a lever and a rod linkage to the accelerator pedal.

(1) Injector operating cam
(2) Idle mixture adjustment
(3) Throttle actuated lever with a link to the throttle plate shaft (8)
(4) Injector plunger
(5) Spray nozzle
(6) Venturi
(7) Moveable lever pivot point adjusted by cockpit control dial
(8) Throttle plate shaft
(9) Throttle plate
(10) Cockpit pressure gauge
(11) Idle pressure adjust
(12) Rubber diaphragm within an assembly added to the pump
(13) Bleed screw
(14) Relief valve, with rubber seal (14a). The nut (14b) is fixed from rotating within the sealed housing, but is free to move vertically
(15) Fuel pump
(16) Check valve
(17) Priming pump
(18) Lever plate (19) pivot
(19) Lever plate pivoted to adjust moveable pivot (7) about (18)
(20) Coarse thread rotated by shaft (22) moving lever plate (19)
(21) Link to lever plate
(22) Shaft to cockpit control dial
(23) Rod to throttle pedal
(24) Shaft to cockpit idle adjust
(25) Vacuum line
(26) Pressure fuel line

The Lycoming fuel injection system in its final form. Refer also here
Editor: - Fuel pump pressure at idle is set by means of the idle pressure adjuster (11), which alters spring pressure on the relief valve. When the throttle is opened and vacuum developed via the venturi is applied to the underside of the diaphragm, pressure on the valve is increased above the pressure at idle as delivered by the spring alone. This arrangement results in a progressive increase in fuel pressure above that set at idle, in accordance with increased inlet manifold airflow.

Idle mixture is set separately from fuel pump pressure at idle, by means of the adjusting screw (2), and idle speed is controlled by adjuster (24).

An increase in fuel pressure at idle will result in a richer idle mixture. To compensate for this the nozzle must be closed, via idle the mixture adjuster, so as to reduce the mixture. It is important to note that this adjustment has the secondary effect of also reducing the mixture when the nozzle is in the full throttle position. Alternatively reducing idle pressure will result in an increase in the mixture at full throttle. This phenomenon may well cause some confusion.

The cockpit mixture control provides a ready method of mixture adjustment for testing while underway, and a dial scale on the control knob will provide a nominal indication of the degree of any adjustment. Ralph's method of making tests at full throttle, under various conditions of engine load, in order to set the fuel pressure at idle, will be seen to be logical.

When Ralph owned the car the fuel system was proven efficient and reliable. It would appear that subsequently there has been problems due to some aspects not being fully understood.

This clever one off design was developed to eliminate possible float chamber fuel surge and or fuel vapour locks, as well as the high bonnet line or intrusive bulge required had a carburettor been fitted. A cold air duct was incorporated out of sight on the underside of the bonnet, to draw cold air from the high pressure area behind the front grill.

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