Fuel Delivery and Air Induction: Service and Repair

Venting of injection system

Venting fuel filter

Model 115.1







1 Loosen venting screw (2) or with fuel filter with- out venting screw loosen hollow screw (2 and 4).

Model 123.1




Loosen hollow screw (3) and keep pumping with hand pump until fuel pumps out free of bubbles. Tighten hollow screw again.




2 Loosen actuating button (3) of manual delivery pump (on engine 617 in model 115.1 not required) and keep actuating manual delivery pump until fuel emerges free of bubbles at vent screw (2) or hollow screw (2 and 4). Tighten vent screw or hollow screw again.


Venting injection pump




3 M-injection pump with pneumatic governor. Loosen vent screw (arrow) on injection pump and also keep pumping with hand pump until fuel emerges free of bubbles. Tighten vent screw again.




4 MW and M/RSF-injection pump with mechanical governor. Keep pumping with hand pump until overflow valve on injection pump opens (audible buzzing noise).

5 Tighten actuating button of manual delivery pump again.

Note: This will force pump piston on a sealing ring and the hand pump is sealed in outward direction. With actuating button released, the manual delivery pump will leak during operation and air may enter fuel system.

6 Run engine and check whether all connections are leaktight.