106
FUEL SYSTEM
CARBURETOR OPERATION
Accelerator Pump
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
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.
AIR
FUEL+AIR (MIXTURE)
FUEL
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