PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620
- LESSON 1/TASK 2
FIGURE 15. IDLE AND LOWSPEED SYSTEMS.
(b) As the throttle valve is opened, the vacuum under it begins to
fall off, causing less gasoline to be drawn from the idle port. As more air
flows through the throat, the gasoline will begin flowing through the low
speed or offidle discharge port, which is usually in the shape of a
rectangular slot or a series of two or three holes. During the lowspeed
system operation, there is still not enough airflow through the throat for
the discharge nozzle to work.
(3) Idle Mixture Screw. A needle shaped screw is used in the
carburetor to regulate the idle port opening. The airfuel ratio of the
idle system can be adjusted by turning the screw in or out.
(4) Air Bleeds. Air bleeds also are used in the idle and lowspeed
circuits to help atomize the fuel.
(5) Passage to Float Bowl. The passage that supplies the idle and
lowspeed circuits must (at some point) be higher than the level of the
gasoline in the float bowl. If this passage went straight to the idle and
lowspeed ports, the float bowl would be able to drain through them.