0348389 JOHNSON *DECAL, Rear, 175

Illustration 1 g00682168
Fuel Flow Schematic
(1) Fuel filter housings.
(2) Fuel return line.
(3) Fuel injector
(4) Fuel supply line.
(5) Check valve
(6) Fuel filter change valve
(7) Check valve
(8) Fuel supply manifold
(9) Fuel return manifold
(10) Fuel pressure control valve
(11) Fuel supply line.
(12) Check valve
(13) Fuel transfer pump
(14) Check valve
(15) Hand priming pump
(A) Fuel supply
(B) Fuel return Fuel transfer pump (13) is located on the left rear side of the front housing. The fuel transfer pump is powered by a spur gear that is mounted on the engine oil pump drive gear.The fuel transfer pump has a check valve and a bypass valve. The check valve prevents fuel flow back through the fuel transfer pump. The bypass valve limits the maximum pressure of the fuel. The bypass valve will open the outlet side of the pump if the fuel pressure is greater than 700 kPa (101 psi). This helps prevent damage to the fuel system components. The fuel system components can be damaged by too much pressure.Fuel from the supply tank is pulled through the primary fuel filter (if equipped) by the fuel transfer pump. From the fuel transfer pump, the fuel is then sent to the check valve (12).The check valve (12) prevents fuel flow back through the fuel transfer pump when a hand priming pump (15) is used.The fuel transfer pump pushes the fuel through the following components:
Check valve (12)
Fuel filter change valve (6)
Fuel filter housings (1)
Fuel supply manifold (8)
Illustration 2 g00563926
Fuel Flow Through The Cylinder Head
(3) Fuel Injector. (C) Fuel return. (D) Fuel supply.
The fuel flows through the manifold to the fuel supply line (4) on the right side of each cylinder head. A drilled passage in the cylinder head directs the fuel to a circular chamber around each fuel injector (3). The chamber is made by the mating fit of the following components:
O-ring seals on the outside of the fuel injector
The bore for the fuel injector in the cylinder headOnly part of the fuel is used for injection. The remaining fuel flows through the chamber to a drilled passage on the left side of the cylinder head. This passage is connected by a fuel return line (2) to the fuel return manifold (9). This constant flow of fuel around the fuel injectors helps to cool the fuel injectors.The fuel flows through the fuel return manifold (9) to fuel pressure control valve (10). The fuel pressure control valve is located on the right side of the front housing. The fuel flows through the fuel pressure control valve. Then, the fuel flows back to the supply tank.The fuel pressure control valve keeps the pressure in the fuel system at 430 to 670 kPa (62 to 97 psi). The fuel is regulated at this range of pressure when the engine is at rated speed.The check valves (5) and (7) prevent fuel flow back into the fuel filter housing when the fuel filters are changed. It will be necessary to use a hand priming pump (15) to force air from the fuel system when the filters are changed. The hand priming pump (15) must be used when the fuel lines are dry. For example, use the priming pump after an overhaul or other major fuel system maintenance. A check valve (14) prevents fuel flow back through the hand priming pump when the engine is running.