Fuel from the tank flows through the fuel line to the diaphragm pump.
It is driven by the camshaft eccentric, which acts on the pump drive lever.
A fine brass mesh filter is fitted in the pump inlet union.
When the engine is not running, fuel is pumped to the carburettor by the manual drive lever of the pump.
In the lower part of the pump body there is a hole for checking the integrity of the fuel pump diaphragm.
Removal and dismantling of the fuel pump
We conventionally remove the pump from the engine removed from the vehicle.
Using a 12 mm socket, we unscrew the two fuel pump mounting bolts.
We remove the fuel pump.
We remove the fuel pump gasket.
We mark the mutual position of the cover and the body parts of the fuel pump.
Using a flat screwdriver, we unscrew two screws.
We remove the cover.
We remove the sealing gasket.
We remove the mesh filter.
Using a screwdriver, we unscrew the eight screws holding the body halves together.
We separate the pump body.
Using an 8 mm spanner, we unscrew the rod nut while holding the upper diaphragm washer with adjustable pliers.
We remove the upper washer, three diaphragms, the lower washer and the spring.
If only the diaphragms are damaged, we replace them and reassemble the pump in the reverse order.
For complete dismantling of the pump, we remove the diaphragm thrust washer from the rod.
We extract the spring thrust washer.
Using a 9 mm spanner, we unscrew the two screwed plugs.
With a thin punch, we drive out the pump drive lever axis.
We extract the drive lever, the lever bush and the spring.
We extract the rod with its seal.
If damaged, we replace the rubber seal.
Inspection and fault diagnosis
Wash all pump parts in petrol.
Inspect the pump body. The threaded holes of the body must not be damaged or have stripped threads.
On the pump head mounting flange there must be no warping in the area of the threaded holes.
The mesh filter of the control hole must not be clogged or damaged.
Inspect the diaphragm. If it has cracks, tears or significant scuffing, it must be replaced.
Replace the torn mesh filter.
Check whether the valves in the pump head are sticking.
If sticking is present, eliminate the causes or replace the fuel pump head.
It is more convenient to assemble the pump in the following sequence:
We fit the thrust washer, spring, diaphragms and diaphragm washers onto the rod.
We tighten their mounting nut.
We fit the rod with the diaphragms into the pump body and, having sunk the rod, insert the lever with its bush and spring.
The lever fork must engage with the rod (as shown in the photograph).
We carry out the further assembly of the pump in the reverse order.
When screwing in the screws connecting the body halves, we align the marks and press the manual drive lever upwards so that the diaphragms deflect and the holes of the diaphragms and the body coincide.
Sealing the outlet union with a finger, we create pressure with the manual drive lever, having lowered the pump inlet union into the fuel.
After holding for 10–15 s, we release the finger. Fuel must squirt out of the outlet union.
Otherwise, we tighten the screws connecting the pump body and cover and check the serviceability of the pump again.
If we have not managed to restore the serviceability of the pump in this way, the valves are leaking.
In this case, we replace the pump as an assembly or the body half with the valves.
We fit the pump in the reverse order.
In the pump body there is a drain hole for draining fuel if the diaphragms are damaged.
Therefore, after starting the engine and during its operation, the absence of fuel leakage from this hole of the fuel pump should be monitored.
