FUEL SYSTEM
CARBURETOR OPERATION
Accelerator pump
Only 15 HP models are equipped with an accelerator pump system.
When
quickly accelerated, the engine draws a large volume
of
air with fuel lagging behind causing the
mixture to be transitionally
lean.
The accelerator pump compensates for such a fuel deficiency. This is a plunger type pump that pressure
feeds
fuel, at the time of quick acceleration, to the acceleration pump nozzle, which sprays fuel into the
main bore. With this provision, the engine can
be
accelerated smoothly.
Operation
of
acceleration pump
When the throttle lever is opened quickly, the accelerator pump lever moves
in
the direction indicated by
the arrow with spring force causing the
plunger to be depressed. Because the lower check valve closes
due to pressure,
fuel inside the accelerator pump chamber forces the upper check valve open, causing
fuel to be sprayed to the main bore through the acceleration nozzle.
When the
throttle lever returns, the accelerator pump lever moves
in
the opposite direction of the arrow,
which causes the
plunger to
be
returned by the force of lower spring. At this time, the upper check valve
is closed by spring force and the lower check valve opens, allowing fuel to enter the accelerator pump
chamber.
1. Accelerator pump lever
2. Plunger
3. Acceleration nozzle
4. Lower check valve
5. Upper check valve
6. Spring
7.
Spring
8. Throttle lever
9. Lower spring
110
¢=I AIR
...
FUEL +AIR (MIXTURE)
...
FUEL
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