FUEL SYSTEM (Fig. 19.01)
The fuel tank is mounted below the luggage compartment floor. To gain access, lift carpet and right-hand panel of floor.
An S.U. electrical fuel pump is used in the system and is situated behind luggage compartment panels above the wheel arch on the right-hand side. For full details of the pump see Electrical Section.
Fuel filter (Fig. 19. 1 0)
A fuel filter is situated adjacent to the suspension turret at the right-hand side of the engine compartment and must be changed every 12,000 miles.
Twin Zenith C.D.S. 175 carburettors are mounted on a pyramid casting which in turn is attached to the inlet manifold.
The carburettors used are of the same type used on the GT6 Mk. 11 and as such may be serviced by following instructions given in the manual with the following exceptions.
Control of throttle, choke and kick-down (automatic transmission only) is by cable from their respective control points to the carburettors.
The throttles on the carburettors are inter-connected to provide synchronized operation by a spring-loaded operating lever centrally mounted and connected to each carburettor by link rods.
Setting procedure Set slow running adjustment screws to 21 threads below bracket. Insert a 5 mm. (3/16th in.) dia. bar through mounting bracket and operating lever slot as shown in Fig. 19.02. Fit fixed length link rod (6) to the ball joints on right-hand carburettor and operating lever. Adjust the other link rod (7) to the distance between left-hand carburettor and operating lever ball joints, fit rod and tighten locknut. Position driving tag of slave lever (1) at the left-hand side of the slot in operating lever (2). Position outer throttle cable through abutment (3) and thread inner cable along guide (4). Thread inner cable into swivel pin (5), tighten clamp screw to cable holding relative positions of levers and ensuring that the cable is not tight (pulling pedal) or slack (allowing tag to move along the slot when released).
The choke control knob operates twin cables connected to a starter box on each carburettor. The starter box type of choke is not described in the current GT6 Manual. A brief outline of this system is as follows.
Upon operation of the choke control, a lever on the side of the carburettor rotates a disc in the starter box. In the disc a set of holes of different diameters are drilled. When the disc is fully rotated, the largest hole is in communication with the starter circuit and provides the richest mixture. Fuel is drawn from the float-chambers via a vertical drilling adjacent to the central main fuel channels through the starter box and into the throttle body on the atmospheric side of the throttle plate.
A cam, externally mounted on the choke lever, moves in conjunction with the starter disc, operating the throttle beyond the normal idle position to provide fast idle speed when the engine is cold. Progressively pushing in the choke rotates the disc and cam, bringing smaller holes in communication with the starting circuit thus weakening the mixture, while the cam allows the throttle linkage to return to the normal idling position.
Carburettor jet needle adjustment
The adjustment of air/fuel ratio is now through the top of the carburettor, using tool S353 as illustrated. The effect of this modification is that the needle is moved in relation to the jet which is now fixed.
Adjustment of air/fuel ratio Remove the carburettor dampers (Fig. 19.07) and insert the adjusting tool carefully to avoid spilling the dashpot oil. Turn the outer tool to engage its lug in the recess of the air valve tube. Turn the inner bar to engage with the hexagon in the screw adjustment at the bottom of the air valve tube .(Fig. 19.06) Hold the outer tool and turn the inner bar clockwise to enrich the mixture and anti-clockwise to weaken the mixture. (Fig. 19.08) It is important to adjust both carburettors equally and to synchronize the throttle settings afterwards. Never attempt to set carburettor needles without appropriate equipment to measure the air/fuel ratio. After use, remove the tool, top up dashpots and refit dampers.
CARBURETTORS-REMOVE AND REFIT
NOTE: It is convenient whether one or both carburettors are to be removed to take off the pair complete with air cleaner, induction pipes, mounting pedestal and inter-connecting linkage.
1 . Disconnect the fuel feed pipes from carburettors. 2. Disconnect the crank case breather pipe from the rear right-hand camshaft cover. 3. Disconnect the choke cables. 4. Disconnect the accelerator cable. 5. Disconnect the vacuum pipe from left-hand carburettor. 6. Remove the vacuum advance union from left-hand carburettor. 7. Remove the centre retaining nut and washers. 8. Disconnect air cleaner elbows from carburettors. 9. Lift off carburettors complete with mounting bracket. (Fig. 19.03) 10. Refit carburettors, reversing above procedure. NOTE: An "O" ring seal is interposed between mounting bracket and inlet manifold. Check serviceability before refitting.
AIR CLEANER-REMOVE AND REFIT
1 . Release two securing clips and lift off top casing. 2. Lift out element. 3. Remove six bolts securing air cleaner to air induction pipes. 4. Lift off air cleaner and two gaskets. 5. Refit by reversing above, but noting: Fit gaskets, then the six bolts loosely before tightening to the correct torque figure. Ensure that the element and the clip of the top cover are correctly positioned before attempting to secure retaining clips.
AIR CLEANER-RENEW ELEMENT (Fig. 19.09)
1 . Release two securing clips and lift off top casing. 2. Lift out element. 3. Fit new element in position. 4. Refit top cover ensuring that the rear clip is engaged correctly and that the two clips make a secure fitting.