PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
FIGURE 34. UPDRAFT, DOWNDRAFT, AND
SIDEDRAFT CARBURETORS.
i. Degasser System. The degasser system is designed to shut off the
supply of fuel to the idle circuit whenever there is high manifold vacuum,
such as periods of deceleration, preventing large amounts of fuel from being
drawn into the engine through the idle port. The degasser consists of a
needle valve, a spring that holds the needle valve open, and a vacuum
diaphragm that operates the needle valve through a fulcrum. The diaphragm
is operated by a manifold vacuum. During periods of normal engine idle, the
manifold vacuum is not high enough to operate the diaphragm and the needle
valve remains open. During periods of deceleration, the manifold vacuum is
high enough to cause the diaphragm to close the needle valve, shutting off
the idle system. The needle valve can also be closed by pushing a button on
the instrument panel to energize a solenoid, closing the needle valve. The
purpose of this manual actuation device is to clear the idle circuit and
manifold of unburned gases before the engine is turned off.
j. Accessory Systems. There are numerous devices that are used on
carburetors to improve driveability and economy. Their application varies
from vehicle to vehicle. The following paragraphs list the most common of
these devices.
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