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6. THROTTLE BODY
6-1 SPECIFICATIONS
This engine is equipped with Electronic Fuel Injection system (FI system) integrated with ECU
(Engine Control Unit).
The FI system consists of throttle body (2-barrel), ECU, MAP (Manifold Air Pressure) sensor,
injector, pressure regulator, temperature sensor, electric fuel pump, and pulsation damper.
The fuel system is calibrated after careful testing for optimum all-round performance (including
starting, acceleration, fuel consumption, output power characteristics).
The throttle body monitors air and engine temperature at start up and performs the choke
function automatically.
While the engine is in operation, the throttle body monitors engine speed, manifold air pressure,
and engine temperature to ensure proper engine performance.
6-2 FUNCTIONS AND CONSTRUCTION
6-2-1 ELECTRIC FUEL PUMP
The electric fuel pump is located below the throttle body, and actuated by power from the DC
battery. The fuel flows from the tank into the fuel pump. When the fuel pump is actuated by DC
battery, the fuel is pressurized by the pump and pushed into the throttle body pressure port.
6-2-2 FUEL PRESSURE REGULTOR
After the fuel pressure port is a diaphragm-type fuel pressure regulator.
The fuel pressure regulator relieves the throttle body of any excess fuel pressure and returns
excess fuel pressure back to the fuel tank through the fuel pressure return pipe.
6-2-3 FUEL INJECTOR
The throttle body pressure port feeds fuel at a regulated pressure to the fuel injectors.
Fuel is metered by the fuel injector that is actuated electronically by ECU.
The fuel is injected into the throttle bore and mixed with air from the air cleaner.
6-2-3 ENGINE CONTROL UNIT (ECU)
The ECU (engine control unit) on bottom of the throttle body is powered by DC battery. The
ECU monitors engine conditions such as engine speed, air pressure, and engine temperature.
With these inputs, the ECU actuates the fuel injector to ensure the fuel/air mixture is of optimum
concentration and is fed into the combustion chamber of the engine at the correct timing. When
engine speed reached to 4,200 rpm, the ECU cuts fuel to prevent over speed.
The ECU also controls the low oil sensor system and monitors voltage of DC battery, and each
wiring whether disconnecting or electrical short circuit.
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