the inlet valve (20) into the pumping chamber (21). When the armature has traveled well towards the end of its stroke the throw-over mechanism operates and the outer rocker moves rapidly backwards, thus separating the contact points and breaking the circuit. The armature and diaphragm will now move away from the coil under the influence of the diaphragm spring, thereby expelling the fuel through the outlet valve at a rate determined by the requirements of the engine. As the armature approaches the end of its stroke, away from the coil, the throw-over mechanism again operates, the tungsten points remake contact, and the cycle of operations is repeated.
DIAPHRAGM AND CONTACT BREAKER SETTINGS—See Fig. 1.
If the diaphragm has been disturbed It is necessary to reset the position of the diaphragm spindle in the rocker trunnion (25). This is done as follows the screw securing the spring blade (1) should be slackened and the blade swung to one side so that the points no longer make contact. Holding the coil housing (6) in the left hand, screw the diaphragm (36) in a clockwise direction with the thumb of the right hand, alternately pressing and turning until the rocker throw-over ceases. Unscrew the diaphragm one-sixth of a turn at a time In the same manner, slowly pressing and turning, until the rocker throw-over mechanism just operates at this point continue unscrewing until holes are in line and then unscrew a further 2/3rds of a turn (four holes). Assemble the coil housing (6) to the main body (17); the six screws which hold the coil housing to the body may then be replaced and tightened. It is now necessary to check that the top of the inner rocker (27) has made contact with the end face of the coil housing as indicated at (5). If there is a visible or measurable gap, the six screws should be slackened off and then retightened until this condition of contact at (5) is achieved. The spring blade (1) (previously sprung to one side) should now be replaced in its normal position. The slot in this is provided with an adequate clearance round its attachment screw; this allows it to be repositioned SQ that when the outer rocker (3) operates to make or break the contact between the tungsten points one pair of points wipes over the centre-line of the other pair in a symmetrical manner. The rocker mechanism and spring blade should be set so that when the outer rocker (3) is pressed onto the coil housing the spring blade rests on the narrow ridge which projects above the pedestal mouldIng (2). In this position the gap between the points should be 030 in. (.76 mm.). When the outer rocker is released the spring blade should be deflected away from the ridge, if necessary, the blade and/or rocker fingers can be set to achieve this position.
|
FAULT DIAGNOSIS
1. Suspected fuel feed failure
Disconnect the fuel line at the carburettor and check for flow.
(a) If normal, examine for obstructed float-chamber needle seating or gummed needle.
(b) If normal initially, but diminishing rapidly and accompanied by slow pump operation, check for correct tank venting by removing the filler cap. Inadequate venting causes a slow power stroke, with resultant excessive burning of contact points.
(c) If reduced flow is accompanied by slow operation of the pump, check for any restriction, on the Inlet side of the pump, such as a clogged filter, which should be removed and cleaned. In the case of reduced flow with rapid operation of the pump, check for an air leak on the suction side, dirt under the valves, or faulty valve sealing washers.
(d) If no flow, check for:
(i) Electrical supply
Disconnect the lead from the terminal and touch it against the body of the pump; if a spark occurs current is available and earthlng of the pump is satisfactory.
(ii) Faulty contact points
If electrical supply is satisfactory the bakelite cover should be removed to check that the tungsten points are in contact. The lead should then be replaced on the terminal and a short piece of bared wire put across the contacts. If the pump then performs a stroke the fault is due to dirt, corrosion, or malad-justment of the tungsten points.
(iii) Obstructed pipeline between fuel tank and pump The inlet pipe should be disconnected; if the pump then operates, trouble is due to a restriction in the pipeline between the pump and the tank. This may be cleared by the use of compressed air after removing the fuel tank filler cap. IT SHOULD BE NOTED, HOW-EVER, THAT COMPRESSED AIR SHOULD NOT BE PASSED THROUGH THE PUMP AS THIS WILL CAUSE SERIOUS DAMAGE TO THE VALVES.
(iv) Faulty diaphragm action
If the previous operations fall to locate .the trouble, stiffening of the diaphragm fabric or abnormal friction in the rocker throw-over mechanism is to be suspected, To remedy these faults the coil housing should be removed and the diaphragm flexed a few times, taking care not to lose any of the 11 rollers under it. Prior to reassembly it is advisable to apply a
|
**
