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4-22 FUEL SYSTEM
ACCELERATION SYSTEM
Acceleration pump
Only DF15 model is equipped with an accelerator pump system.
When quickly accelerated (opening the throttle valve quickly), the engine suctions a large volume of air with
fuel lagging behind causing the mixture to be transitionally lean.
To compensate for such a fuel deficiency, an acceleration pump device is provided. This is a plunger type
pump that pressure feeds fuel, at the time of quick acceleration, to the acceleration pump nozzle from which
fuel is sprayed into the main bore preventing the mixture from becoming lean. With this provision, the engine
can be accelerated smoothly.
Operation of acceleration pump
When the throttle lever
8
is opened quickly, the acceleration pump lever
1
moves to the direction indicated
by the arrow with the spring
7
force causing the plunger
2
to be depressed. Because the check valve
4
closes due to pressure, fuel inside the acceleration pump chamber forces the check valve
5
open causing
fuel to be sprayed to the main bore through the acceleration nozzle
3
.
When the throttle lever
8
returns, the acceleration pump lever
1
moves to the direction opposite to the
arrow, which in turn causes the plunger
2
to be returned by the force of spring
9
. At this time, the check
valve
5
is pulled back to close by the force of spring
6
and the check valve
4
to open allowing fuel to enter
the acceleration pump chamber.
AIR
FUEL+AIR (MIXTURE)
FUEL