Figure 40. Fuel pump:
1 - discharge pipe; 2 - filter; 3 - upper body; 4 - suction pipe; 5 - lid; 6 - suction valve; 7 rod; 8 - manual fuel pumping lever; 9 - spring; 10 cam; 11 - balance beam; 12 - lever of mechanical fuel pumping; 13 - lower body; 14 - internal spacer gasket; 15 - spring spacer; 16 - discharge valve.
The fuel pump consists of a lower housing 13 with drive levers, an upper housing 3 with valves and pipes, a diaphragm unit and a cover 5. Three diaphragms are installed between housings 3 and 13: two upper ones — working ones — for fuel supply, a lower one — safety one — to prevent fuel from entering the drive housing if the working diaphragms are damaged. The diaphragms are made of membrane fabric. Between the working and safety diaphragms, there are outer 15 and inner 14 spacer gaskets. The outer gasket has an opening for fuel to exit if the working diaphragms are damaged. The diaphragms with plates are installed on the rod 7 and fastened from above with a nut. There is a compressed spring on the rod under the diaphragm unit. The rod with a T-shaped tailpiece is inserted into the slot of the balancer 11, which allows the diaphragm unit to be removed without disassembling.
Levers 12.8 and balancer 11 are installed in the lower housing. Valves are installed in the upper housing 3: suction 6 and discharge 16. Gaskets made of diaphragm material are placed under the valves. The valves are pressed against the seats by springs. Cover 5 is attached to the pump housing from above with a central bolt. A plastic mesh filter is installed between the cover and the housing. Upper housing 3 has discharge 1 and suction 4 pump branches.
When the engine is running, the camshaft eccentric acts on the lever 12 via the pusher and turns the balancer 11, which pulls the pump diaphragms. In this case, the diaphragm spring is compressed. The diaphragms create a vacuum, as a result of which the fuel through the suction valve 6 fills the working cavity of the pump above the diaphragms. When the eccentric runs off the pusher, the lever 12, balancer 11 and the rod with diaphragms are released. The diaphragms, under the action of the spring, create pressure in the working cavity, close the suction valve 6 and through the discharge valve 16 supply fuel to the carburetor.
With low fuel consumption, the diaphragm stroke is incomplete, so the stroke of the lever with the balancer will be partially idle.
Fuel supply by lever 8 of manual pumping is carried out by the action of cam 10 on balancer I and diaphragm of fuel pump.
A heat-insulating spacer and adjusting gaskets are installed between the pump and the drive housing. For correct installation of the pump, two of the three gaskets listed below are used: gasket A — 0.27...0.33 mm thick; gasket B — thickness 0.7...0.8 mm; gasket C — 1.1...1.3 mm thick. The installation diagram is shown in Figure 41.
The pump is installed in the following order. Install the heat-insulating spacer, placing gasket A under it, and place gasket B on the plane in contact with the pump. Measure the distance d (the minimum amount by which the pushrod protrudes, determined by slowly turning the crankshaft). If the size d is within 0.80...1.30 mm, then the pump is attached to the engine; if d is less than 0.80 mm, gasket B is replaced by gasket A; if d is greater than 1.30 mm, then gasket B is replaced with gasket C. Measure the dimension d again and attach the pump to the engine.
There must always be a gasket A between the drive housing and the heat-insulating spacer.