Honda CBR650F Service Manual page 46

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TECHNICAL FEATURE
FUEL FILL CAP BREATHER
The fuel tank breather function of this model is controlled by the two one-way valves (positive and negative pressure valves) in the
fuel fill cap as a substitute for a conventional vapor-liquid separator in the fuel tank.
COMPONENT FUNCTION
VALVES
Regulate the internal pressure of the fuel tank (they are closed with the spring
until each specified pressure). In addition, spilling fuel to the outside is reduced when a fall-down has occurred.
BREATHER SEAL
The connecting section of the fuel fill cap and tank of the breather passage is prevented from leaking.
VALVE OPERATION
POSITIVE PRESSURE VALVE:
When the tank internal pressure increases by fuel vapor, the positive pressure valve opens to release excess pressure out of the
tank.
NEGATIVE PRESSURE VALVE:
When the tank internal pressure decreases (fuel consumption etc.), the negative pressure valve opens and introduces air (TH
model) including stored fuel vapor in the EVAP canister) into the tank.
When increasing pressure:
POSITIVE PRESSURE
VALVE (Open)
When decreasing pressure:
(Close)
• When opening the fuel fill cap, it will be sounded for pressure releasing, but it is not blockage of the passage. If checking for
clogs in the fuel tank side passage is necessary, apply air pressure to the breather hose end while opening the fuel fill cap.
• Always replace the breather seal with a new one when the fuel fill cap is removed for service.
• Check the breather seal for deterioration, cracks or damage in accordance with the maintenance schedule "Evaporative
Emission Control System (TH model)" (page 3-12).
(Close)
NEGATIVE PRESSURE
VALVE (Open)
GENERAL INFORMATION
FUEL FILL CAP
BREATHER PIPE
(in fuel tank)
BREATHER SEAL
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