THE FUEL SYSTEM and the tank. This may be cleared by the use of compressed air after removing the fuel tank ller cap. It should be noted, however, that compressed air should not be passed through the pump as this will cause serious damage to the valves. (iv) Faulty diaphragm action In the event of the previous operations failing to locate the trouble, it may be due to a stiffening of the diaphragm fabric or the presence of abnormal friction in the rocker throwover mechanism, or a combination of both. To remedy/these faults the coil housing should be removed and the diaphragm exed a few times, taking care not to lose any of the 11 rollers under the diaphragm. Prior to this resetting it is advisable to apply, very sparingly, a little thin oil to the throw-over spring spindles at the point where they pivot in the brass rockers. The diaphragm/armature assembly should then be reassembled in accordance with instructions given under that heading. 2. Noisy pump If the pump is noisy in operation, an air leak at the suction line may be the cause. Such a leak may be checked by disconnecting the fuel pipe from the car- buretter and allowing the pump to discharge into a suitable container with the end of the pipe submerged. The emission of continuous bubbles at this point will 2 . r a I 3 O 0 We 6 5 g 7 A509SIW Fig. D.9 The HS4 carburetter 1. Jet adjusting nut. 5. Float-chamber securing nut. 2. Throttle stop screw. 6. Jet link. 3. Choke or fast-idle screw. 7. Jet head. 4. Jet locking nut. 8 Vacuum ignition take-o'. MGB. Issue 5. 69615 'lf/ ; s \ s Wis Immmmr yllllIIIIIIIIIIIIIIIIIIIIIIIIIII K t g\\\\\{\\\\ l so // C: ///l, . I I // V/l/[l/l/l/l s WAIV/l/ k \\\\\\\\\\\\\\\\\\ 'r\\\\\ ////l///l ; i? Ill/II/A //4 3 4 A 6 2 7 9 Fig. D. 10 A sectional view of the HS4 carburetter 1- J 103? nut. 5. Piston lifting pin. 2- Jet adjusting nut. 6. Needle securing screw. 3. 10 head. 7. Oil damper reservoir. 4. Feed tube from oat- chamber. conrm the existence of an air leak. The fault should be rectied by carrying out the following prOCedure: (a) Check that all connections from the fuel tank to the pump are in good order. (b) Check that the inlet union is tight" and that the sealing O ring is not damaged. (c) Check that the coil housing securing screws are well and evenly tightened. Air leaks on the Situation side cause rapid operation of the pump and are the most frequent cause of premature failure. 3. Pump operates without delivering fuel If the pump operates continuously without delivery of fuel the most likely causes are: (a) A very serious air leak on the suction side or, (b) Foreign matter lodged. under one of the valves, particularly the inlet valve. To remedy (a) see Section 2 (above) In order to remove any foreign matter lodged under the valves, these should be removed for cleaning and great care taken that the plastic material of the valve disc is not scratched or damaged during this operation. 131 D.9