Yamaha F50A - Technical Tips; Carburetor

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Technical tips
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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.
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Prime Start
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Intake manifold of the engine
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Thermo heater plunger
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Fuel enrichment valve
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To carburetor #2 or #4
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Carburetor
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Intake silencer
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Air
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Fuel
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Plunger movement
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S62Y1240
Features and benefits / Technical tips