Honda LEAD 110 2009 Service Manual page 40

COMPARISON BETWEEN CARBURETOR AND PGM-FI SYSTEM
BASIC OPERATION FROM IDLE TO HIGH SPEED
BASIC OPERATION:
Carburetor and PGM-FI system controls the power output of engine by regulating the volume of fuel/air mixture intro-
duced into engine by means of opening/closing the throttle valve. They both are designed to provide an ideal air-fuel ratio
depending on the volume of incoming air.
CARBURETOR BASIC OPERATION:
• At idle and low speed, with throttle valve in slightly opened position, fuel drawn from pilot screw port (idle port) and
slow port becomes atomized while being mixed with incoming air. The mixture is delivered to the engine.
• In low to intermediate range, vacuum piston rises in accordance with the throttle valve position. Larger the venturi
becomes as the piston lifts up, larger the volume of fuel drawn from the main nozzle and intake air become. The mixture
of atomized fuel from the main nozzle/slow port and intake air is delivered to the engine.
• On high speed, with the vacuum piston and throttle valve in fully opened position, venturi size becomes the largest.
Thus maximum amount of fuel drawn from the main nozzle becomes atomized while being mixed with intake air. The
mixture is delivered to the engine.
SLOW PORT
THROTTLE
VALVE
IDLE PORT
PGM-FI BASIC OPERATION:
• Throughout idle to high speed, preset amount of fuel is discharged from the injector, controlled by ECM which collects
output voltage signals from each sensor, in accordance with the volume of incoming air regulated by the throttle valve.
• The injector discharges proper amount of fuel into the intake manifold, depending on volume of intake air, by adding
corrected fuel discharge duration ( ※ 2) to basic fuel discharge duration ( ※ 1).
※ 1 Basic fuel discharge duration is determined by 2 kinds of Map (page 2-8) memorized in the ECM which looks at
engine revs and volume of intake air (calculated by a preset formula which applies the following: output voltage from
MAP, CKP and TP sensor).
※ 2 Corrected fuel discharge duration is determined by ECM which looks at output voltage from each sensor and mea-
sures the running condition of the engine.
INJECTOR
PGM-FI THROTTLE
BODY (AT IDLE)
CARBURETOR
(AT IDLE AND LOW SPEED)
THROTTLE
VALVE
BASIC DISCHARGE DURATION
CORRECTED
DISCHARGE
DURATION
TECHNICAL FEATURES
VACUUM PISTON
MAIN NOZZLE
THROTTLE
CARBURETOR (ON
VALVE
HIGH SPEED)
INJECTOR
THROTTLE
VALVE
PGM-FI THROTTLE BODY
(ON HIGH SPEED)
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