1. Remove bolt 17 (see fig. Details of the power supply system of the carburetor engine) fasteners and remove the filler neck 18.
2. Unbend the spring clips and remove the air valve 15 from the fuel tank filler pipe.
3. Blow out the valve with air; when lever 1 is in the home position as shown in the figure, valve 2 must be closed. Push lever 1 in the direction of the arrow, the valve should open. If the valve is open or closed in both positions of lever 1, it is defective and must be replaced.