3-22
FUEL SYSTEM
3-22
MODEL
4160
CARBURETOR SYSTEMS (Continued)
IDLE SYSTEM
An idle system supplies the air fuel mixture to
’ operate the engine at idle and low speeds. Idle
fuel enters the system through the main jet into
the main well. Some applications include an idle
tube in the main well to meter the fuel. Other
applications use a horizontal passage from the
main well to the idle well and an idle channel
restriction for metering purposes. The restriction
has been installed in several different locations.
In either type, air enters the idle’ air bleed and
mixes with the fuel after the fuel flows through
the idle tube or restriction. At curb idle the thbot-
tle valves are almost closed. This creates a high
vacuum below the throttle valve with near atmo-
spheric pressure above the valve. As the throttle
valves are opened the transfer slot is pro-
gressively exposed to vacuum and the air-fuel
emulsion is also discharged from the transfer
slot. The air-fuel mixture from the idle passage
IDLE AIR BLEED
1 H 1
RESTRICTION
PASSAGE
qf\>d py
\
MAIN JET
l&E
ADJUSTING
NEEDLE
/
‘ELI.
iDLE
H
\
TRANSFER
IDLE
PASSAGE
DISCHARGE
IDLE
,DLE PASSAGE
TRANSFER DISCHARGE
SLOT
HOLE
CURB IDLE
AIR BLEED
CURB’ IDLE SYSTEM
and the transfer slot supplies the necessary fuel
to operate the engine at lower speeds and
loads.
A low pressure or partial vacuum is created in
the booster venturi and the main metering sys-
tem starts to flow. This moderate opening (tran-
sition) of the throttle is commonly called “tip in.”
When the throttle valves are opened, the accel-
erator pump system mechanically squirts raw
fuel into the venturi to prevent a stumble until the
mixture from the main metering system “catches
up” with the increased air flow. (This supple-
mentary fuel requirement is needed more during
rapid throttle openings.)
A hesitation or “sag” at tip in is one of the
most common carburetor problems. A low fuel
level, a partially clogged idle tube or restriction
gummed-up air bleeds or a manifold leak can
cause a “sag” during tip in. Any problem in the
accelerator pump system will also cause a
problem.
To Next Page
Loading...
Need help?
General
