Accelerator Pump; Air Cut-Off Valve; Reed Valve Inspection; Fuel System - Honda Motorcycle Service Manual

FUEL SYSTEM
ACCELERATOR PUMP
When the throttle valve is opened suddenly, the air-fuel mix-
ture drawn into the cylinder momentarily becomes lean. Be-
cause the vacuum at the venturi drops, air flow at the venturi
slowsdownand thedrawn-upfuel becomes too littlecompared
with the air. To avoid thinning of the mixture under these con-
ditions, an accelerator pump is used for temporary enrichment.
The principle of operation of the pump is as follows:
As the throttle valve is opened, the pump's diaphragm is
depressed by the pump rod. At this time the inlet check valve
is shut, so the pump chamber undergoes a rise in pressure. The
outlet check valve is then opened and fuel is supplied to the
main bore via the pump hole.
As the throttle valve closes, the accelerator pump's diaphragm
is returned by spring action. At this time the inlet check valve
is opened and fuel from the float chamber enters the pump
chamber. The outlet check valve is closed at this point to
prevent air being drawn in through the pump hole.
AIR CUT-OFF VALVE
When the throttle lever is turned in the "close" direction and
*
Throttle valve opens:
I
INLET
/"
CHECK VALVE' A C C E L E R A ~ R PUMP
DIAPHRAGM
Throttle valve closes:
1
engine braking is applied, the fuel mixture becomes lean. An
ignited airlfuel mixture is discharged into the exhaust pipe.
resulting in afterburn. To prevent this afterburn, the air cut-
off valve shuts the air passage to the slow jet to temporarily
make the fuel mixture rich.
With the throttle valve closed and the vacuum in the main bore
increased, vacuum in the air cut-off valve also increases and
moves the diaphragm to shut the air passage.
I
INSPECTION
VACUUM CHAMBER
\
r U I
AIR PASSAGE
This moves to the
left to shut up the
With the vacuum in the main bore decreased, the spring moves
the diaphragm backward and opens the air passage.
REED VALVE
(2-STROKE ENGINES)
Refer to the Model Specific manual for removallinstallation.
/K
; ; ; ; ; w
AIR CUT-OFF VALVE
SPRING
Check the reed valve for fatigue or damage and replace the
reed valve assembly if necessary.
Check the reed valve seat for cracks, damage and clearance
from the reed and replace the reed valve assembly if
necessary.
NOTE
Be sure to replace the reed valve as an assembly.
Disassembling or bending the reed stopper will cause
engine trouble.
REED VALVE
SEAT
Date of Issue : March, 1995
o
HONDA
MOTOR CO.,LTD.
8-7