Yamaha F50 Service Manual
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62Y3A111-6 1 2 3 4 5 6 7 8 I Features and benefits1 Newly designed four carburetors Newly designed four carburetors have been based on the current F50A. Prime Start has been adopted for the starting system to further increase starting performance and serviceability. Further- more, the acceleration pump and the dashpot have been integrated to simplify construction and to ease serviceability. The four carburetors can be accurately and easily adjusted due to the simple construction of the links. 1Prime Start 2Acceleration pump Identification / Features and benefits
GEN INFO General information 1-762Y3A11 CDI unit with microcomputer The ignition system consists of a flywheel, stator, pulser coil, thermoswitch, oil pressure switch, CDI unit, and ignition coil. The CDI unit contains a built-in microcomputer that determines the ignition timing separately for acceleration and for normal operation, based on signals received from the pulser coil, thermoswitch, and oil pressure switch. . 1CDI unit 2Flywheel 3Stator 4Pulser coil 5Thermoswitch 6Ignition coil 7Oil pressure switch 23 4 5 6 7 1 S62Y1210
62Y3A111-8 1 2 3 4 5 6 7 8 I Lower unit Higher class pinion and gears The lower unit of the new T50/FT50B, FT50C uses the same type of large gears that are used in the F100. The use of the same type of gears that are used in a higher class model provides ample dura- bility, making it possible to accommodate a wider range of applications throughout the market. Pinion Forward gear Reverse gear Gear ratio ModelNumber of teethDiameter (mm)Number of teethDiameter (mm)Number of teethDiameter (mm) F50/F50A 13 45 24 74 24 75 1.8 T50/FT50B, FT50C13 46 30 95 30 95 2.3 F50/F50A T50/FT50B, FT50CS62Y1220 Features and benefits
GEN INFO General information 1-962Y3A11 Shift slider type shift mechanism The T50/FT50B, FT50C has adopted the shift slider type shift mechanism. This shift mechanism enables a prompt engagement of the dog clutch regardless of the operating speed of the shift lever. Thus, smooth and positive shift operation has been made possible. 1Shift rod 2Propeller shaft 3Dog clutch 4Shift slider ÈForward ÉReverse
62Y3A111-10 1 2 3 4 5 6 7 8 I Technical tips1 Carburetor Starting system (Prime Start) To facilitate the starting of a cold engine, an air-fuel mixture that is richer than normal is required. For this reason, the Prime Start system has been adopted in the F50/F50A, T50/FT50B, FT50C. In the Prime Start system, the thermo heater plunger is in a position that fully opens the fuel enrich- ment valve while the engine is being started. Thus, fuel enrichment is achieved during the starting of the engine, and continues while the engine is being warmed up. Once the engine starts, current flows from the lighting coil of the to the thermo heater, allowing the wax in the Prime Start unit to expand. The expanded wax moves the thermo heater plunger in the direction to close the enrich- ment valve. As a result, the volume of fuel that passes through the fuel enrichment valve decreases. A few minutes after the engine has started, the thermo heater plunger completely closes the fuel enrichment valve, thus ending the fuel enrichment by the Prime Start system. 1Prime Start 2Intake manifold of the engine 3Thermo heater plunger 4Fuel enrichment valve 5To carburetor #2 or #46Carburetor 7Intake silencer ÈAir ÉFuel ÊPlunger movement : : : 4 5 6 71 2 3 S62Y1240 Features and benefits / Technical tips
GEN INFO General information 1-1162Y3A11 1Prime Start ÈThe enriched air-fuel mixture is delivered to cylinders #1 and #2 by the Prime Start system attached to carburetor #1. ÉThe enriched air-fuel mixture is delivered to cylinders #3 and #4 by the Prime Start system attached to carburetor #3.
62Y3A111-12 1 2 3 4 5 6 7 8 I Carburetor operation 1. Idle and low-speed operation Since the vacuum at the venturi is low when the throttle valve is opened slightly, the main nozzle does not supply any air-fuel mixture to the engine. When the engine is operating at idle, the fuel that passes through the pilot jet and the air that passes through the pilot air jet mix, enabling the air-fuel mixture that has been regulated by the pilot screw to be fed through the pilot outlet. Because the throttle valve opens slightly when the engine is operating at low speeds, air-fuel mix- ture also starts to be fed from the bypass holes. 1Pilot screw 2Pilot outlet 3Bypass holes 4Venturi 5Main nozzle 6Pilot jet 7Main jet 8Pilot air jet9Main air jet 0Throttle valve ÈAir ÉAir-fuel mixture ÊFuel 3 2 2 1 0 9 8 7654 3 : : : S62Y1260 3 2 2 1 0 9 8 7654 3 : : : S62Y1260 Technical tips
GEN INFO General information 1-1362Y3A11 2. Medium speed operation When the throttle valve opens further, air-fuel mixture is fed from the pilot outlet and all the bypass holes. In addition, air-fuel mixture is also supplied from the main nozzle in accordance with the opening angle of the throttle valve. 1Pilot screw 2Pilot outlet 3Bypass holes 4Venturi 5Pilot jet 6Main jet 7Main nozzle 8Pilot air jet9Main air jet 0Throttle valve ÈAir ÉAir-fuel mixture ÊFuel 3 2 1 0 9 8 7 6543 2 S62Y1270 : : :
62Y3A111-14 1 2 3 4 5 6 7 8 I 3. High-speed operation When the throttle valve approaches its fully open position, the fuel that has been regulated by the main jet and the air that has been regulated by the main air jet are mixed in the main nozzle. The resultant mixture is then sprayed by the main nozzle into the venturi. The air-fuel mixture that is sprayed through the venturi is then fed into the engine. 1Pilot screw 2Pilot outlet 3Bypass holes 4Main nozzle 5Pilot jet 6Main jet 7Main air jet 8Throttle valveÈAir ÉAir-fuel mixture ÊFuel : : : S62Y1280 4 5 6 7 812 3 Technical tips
GEN INFO General information 1-1562Y3A11 Acceleration pump The function of the acceleration pump is to ensure a smooth acceleration by preventing the air-fuel mixture from becoming temporarily lean in case the throttle valve is opened suddenly. When the throttle valve is opened suddenly, a large volume of air is introduced into the engine. However, because fuel is heavier than air, it is not possible to supply the volume of fuel that is necessary for the large volume of air that has been introduced. Thus, because it is not possible to achieve the air- fuel mixture that is required by the engine, bucking or hesitation results. For this reason, the acceler- ation pump temporarily increases the fuel volume in order to adjust the air-fuel mixture to a ratio that is necessary for the engine in case the throttle valve is opened suddenly. 1Bypass hose 2Acceleration pump 3Pump chamber 4Diaphragm 1 5Throttle lever ÈAir flow ÉThrottle valve opening direction : : 1 2 3 4 5 S62Y1290