Yamaha F4B - Built-In Primer Pump

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Fuel system
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A
Built-in primer pump
This engine is equipped with a built-in primer pump in order to ease engine starting when the float
chamber is empty, or when operating the engine after it has been stored for a long time.
The built-in primer pump sends fuel directly to the float chamber in the carburetor without operating
the mechanical fuel pump.
A Fuel passage (mechanical fuel pump)
B Fuel passage (built-in primer pump)
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B