Yamaha XT660R, Service Manual

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GEN
INFO
FEATURES
EAS00019
FEATURES
EAS00896
OUTLINE
The main function of a fuel supply system is to provide fuel to the combustion chamber at the opti-
mum air-fuel ratio in accordance with the engine operating conditions and the atmospheric tempera-
ture. In a conventional carburetor system, the air-fuel ratio of the mixture that is supplied to the
combustion chamber is created by the volume of the intake air and the fuel that is metered by the jet
used in the respective chamber.
Despite the same volume of intake air, the fuel volume requirement varies with the engine operating
conditions, such as acceleration, deceleration, or operation under a heavy load. Carburetors that
meter the fuel through the use of jets have been provided with various auxiliary devices, so that an
optimum air-fuel ratio can be achieved to accommodate the constant changes in the operating con-
ditions of the engine.
As the requirements for engines to deliver more performance and cleaner exhaust gases increase,
it becomes necessary to control the air-fuel ratio in a more precise and finely tuned manner. To
accommodate this need, this model has adopted an electronically controlled fuel injection (FI) sys-
tem in place of a conventional carburetor system. This system can achieve an optimum air-fuel ratio
required by the engine at all times by using a microprocessor that regulates the fuel injection volume
according to the engine operating conditions detected by various sensors.
Adoption of the FI system has resulted in a highly precise fuel supply, improved engine response,
better fuel economy, and reduced exhaust emissions. Furthermore, the air induction system (AI sys-
tem) has been placed under computer control together with the FI system in order to realize cleaner
exhaust gases.
1
Air cut-off valve
2
Air induction system
solenoid
3
Engine trouble warn-
ing light
4
Fuel tank
5
Fuel pump
6
Fuel hose
7
Fuel injector
8
Throttle position sen-
sor
9
Intake air temperature
sensor
0
Air filter case
A
Fuel injection system
relay
B
Battery
C
Catalytic converter
D
ECU
E
Lean angle cut-off
switch
F
Fast idle unit
G
Crankshaft position
sensor
H
Coolant temperature
sensor
I
Spark plug
J
Intake air pressure
sensor
K
Ignition coil
1 2 3 4
5 6 7 8 9 0 A
B C
D E F G H I
J
K