Check the fuel supply to the pump. Insufficient filling of the carburetor with fuel can be caused by a malfunction of the fuel pump, as well as clogged or damaged fuel lines and the fuel fine filter.
To determine the cause of the malfunction, disconnect the hose from the discharge pipe 1 (see fig. 14) and using the manual priming lever 8, it is checked whether fuel is supplied. If fuel is not supplied, disconnect the hose from the inlet pipe 4 and check whether a vacuum is created at the inlet of this pipe. If there is a vacuum, then the fuel lines or fine filter are damaged or clogged. If there is no vacuum, the fuel pump is faulty.
The fuel pump can be checked on the stand. By rotating the drive shaft, which has an eccentricity of 1.25 mm, with a frequency (2000±40) rpm, check the pump performance, which should be at least 1 l / min at 20°C. The discharge pressure at zero fuel supply should be 0.21-0.30 kgf/cm2.
In the event of a malfunction, the pump is disassembled and the condition of the parts is checked. All parts must be washed with gasoline and blown with compressed air. Cracks and breaks of body parts are unacceptable. Leakage of the inlet and discharge valves is not allowed. The inlet 4 and discharge 1 branch pipes must not rotate in the seats or have an axial displacement. The diaphragm should not have breaks, delaminations and hardening. The filter must be clean and free of rips. The sealing lip of the filter around the perimeter must be even. Pump valves must not stick.
After checking, all worn parts are replaced with new ones. Damaged pump gaskets are always replaced with new ones and lubricated with a thin layer of grease when installing the pump.