Yamaha MBK MW125 2014 Service Manual

FEATURES1-2EAS20008FEATURESEAS30005OUTLINE OF THE FI SYSTEMThe main function of a fuel supply system is to provide fuel to the combustion chamber at the optimumair-fuel ratio in accordance with the engine operating conditions and the atmospheric temperature. Inthe conventional carburetor system, the air-fuel ratio of the mixture that is supplied to the combustionchamber is created by the volume of the intake air and the fuel that is metered by the jet used in therespective carburetor.Despite the same volume of intake air, the fuel volume requirement varies by the engine operating con-ditions, such as acceleration, deceleration, or operating under a heavy load. Carburetors that meter thefuel 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 conditions of the en-gine.As the requirements for the engine 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 accom-modate this need, this model has adopted an electronically controlled fuel injection (FI) system, in placeof the conventional carburetor system. This system can achieve an optimum air-fuel ratio required bythe engine at all times by using a microprocessor that regulates the fuel injection volume according tothe engine operating conditions detected by various sensors.The adoption of the FI system has resulted in a highly precise fuel supply, improved engine response,better fuel economy, and reduced exhaust emissions.115 12 1113,1496,7,8,2,3 4 5101. Engine trouble warning light2. Lean angle sensor3. Battery4. Fuel pump5. ECU (engine control unit)6. Intake air temperature sensor7. Intake air pressure sensor8. Throttle position sensor9. Crankshaft position sensor10. Ignition coil11. Spark plug12. O 2 sensor13. Coolant temperature sensor14. Injector15. Speed sensor