FUEL RATIO CONTROL

TM 5-2410-237-23

FUEL SYSTEM THEORY OF OPERATION - CONTINUED

0039 00

FUEL RATIO CONTROL - CONTINUED

After the engine is started, engine oil flows through oil inlet (40) into pressure oil chamber (41). From oil chamber (41),

oil flows through oil passage (42) into internal valve (43) and out oil drain passages in stem (38).

Stem (38) will not move until inlet manifold pressure increases enough to move internal valve (43). A line connects the

inlet manifold with inlet air chamber (44) of the air-fuel ratio control.

When inlet manifold pressure increases, it causes diaphragm assembly (45) to move towards the right. This also causes

internal valve (43) to move to the right. When internal valve (43) moves to the right, it closes oil passage (42).

When oil passage (42) is closed, oil pressure increases in oil chamber (41). Oil pressure moves piston (46) and stem (38)

to the left and into the operating position. The air-fuel ratio control will remain in the operating position until the engine

is shut off.

When the governor control is moved to increase fuel to the engine, stem (38) limits the movement of lever (39) in the

FUEL ON direction. The oil in oil chamber (41) acts as a restriction to the movement of stem (38) until inlet air pressure

increases.

As the inlet air pressure increases, diaphragm assembly (45) and internal valve (43) move to the right. The internal valve

opens oil passage (42), and oil in oil chamber (41) goes to oil drain passage (47). With oil pressure reduced behind pis-

ton (46), spring (48) moves the piston and stem (38) to the right. Piston and stem (46 and 38) will move until oil passage

(42) is closed by internal valve (43). Lever (39) can now move to let the fuel rack go to the full fuel position. The air-

fuel ratio control is designed to restrict the fuel until the air pressure in the inlet manifold is high enough for complete

combustion. It prevents large amounts of exhaust smoke caused by an air-fuel mixture with too much fuel.

END OF WORK PACKAGE

0039 00-5