0385803 JOHNSON CARBURETOR ASSY, Lower

Illustration 1 g00849199
Diagram of the basic fuel system (typical example)
(1) Fuel injection nozzle
(2) Fuel return line from fuel injection nozzle
(3) Air inlet heater
(4) Fuel return line from fuel filter
(5) Fuel return line from fuel injection pump
(6) Supply line
(7) Fuel filter
(8) Fuel transfer pump
(9) Water separator
(10) Fuel injection pump
(11) High pressure fuel lines
(12) Fuel tank When the engine is cranking, the fuel is pulled from the fuel tank (12) through the water separator (9) by the fuel transfer pump (8). When the fuel goes through the water separator, any water in the fuel will go to the bottom of the bowl. The fuel transfer pump sends the fuel at a low pressure to the fuel filter (7). From the fuel filter, the fuel goes through the supply line (6) to the fuel injection pump (10).The fuel injection pump sends fuel through the high pressure fuel lines (11) to each of the fuel injection nozzles (1). The fuel injection nozzle sprays fuel into the cylinder. Fuel which is not used by the fuel injection pump goes through the fuel return line (5) to the inlet side of the fuel filter (7). Leakage from the fuel injection nozzles flows through the fuel return line from the fuel injection nozzle (2) to the top of the fuel filter (7), back to the fuel tank (12), and through the fuel return line from the fuel filter (4).The fuel injection pump needs fuel for lubrication. The precision parts of the pump are easily damaged. For this reason, the engine must not be started until the fuel injection pump is full of fuel that is free of air.The system must be primed when any part of the system is drained of fuel. The following list contains examples of both service and repairs when you must prime the system:
The fuel filter is changed.
The fuel line is removed.
The fuel injection pump is removed.Fuel System Components
Illustration 2 g00848385
Fuel system components (left side)
(1) Fuel injection nozzle
(2) Fuel return line from fuel injection nozzles
(3) High pressure fuel lines
(4) Fuel filter
(5) Supply line
(6) Fuel return line
(7) Fuel injection pump
Illustration 3 g00848797
Fuel system components (right side)
(8) Air inlet heater
(9) Fuel transfer pump There is a small filter screen in the fuel transfer pump (9). The pump has a lever which is manually operated in order to prime the fuel system by removing the air. In order to release air from the system, the orifice in the cover of the fuel filter (4) is in the inlet side of the filter. The orifice is connected to the fuel tank by the fuel return line from the fuel filter (4).
If there is no fuel flow through the valve body of the air inlet heater, the fuel injection pump could be damaged. The fuel supply line to the air inlet heater must also be free of air in order to prevent damage.
An air inlet heater that is damaged will allow the fuel to drain into the inlet manifold when the engine is running. This condition could cause exhaust smoke. Excessive fuel could also cause an overspeed condition. An overspeed condition may result in severe engine damage.
The air inlet heater is an electrically operated device. The air inlet heater ignites a controlled amount of diesel fuel in the inlet manifold in order to heat the inlet air. A heater coil in the air inlet heater expands a delivery valve holder in order to allow the fuel to flow into the heater. The fuel is ignited by the hot coil. The combustion heats the air which passes through the inlet manifold when the starter motor is operated.The air inlet heater (8) is installed in the inlet manifold. The air inlet heater is controlled by a remote mounted control switch.Fuel Injection Nozzles
(S/N: 4ZK; 6FK; 7AK; 1ML)
Illustration 4 g00856834
Fuel injection nozzle
(1) Fuel return line
(2) Cap nut
(3) Fuel inlet
(4) Pressure adjusting screw
(5) Spring for pressure adjusting screw
(6) Body
(7) Spindle for spring
(8) Retaining nut for fuel injection nozzle
(9) Needle valve
(10) Nozzle
(11) Orifice
(12) Seat washer Fuel flows