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PART 10-2-
STROMBERG BV-2 CARBURETTOR
10-15
FIG. 2-Carburettor
f
Rear View
needle
valve,
contacting the tab of
the
ftoat and lever assembly, reacts
to any change
in
height of the ftoat
and the fuel level in the ftoat cham-
ber.
IDLE FUEL SYSTEM
The
idle
fuel
system functions
when the engine is operating at low
R.P.M.
It
supplies the fuel-air mix-
ture
when the
air ftow through the
carburettor venturi is insufficient to
operate the main metering
system.
The range of the idle system will
extend
into
the operation of the main
metering
system.
Fuel ftows from the
main channel, up the
idle
tube chan-
nel and through the calibrated idle
tube
assembly.
Filtered air from the
carburettor air horn enters the idle-
air-bleed and mixes with the fuel.
The air bleed also serves as a vent to
prevent syphoning of fuel at high
speeds or when the engine is shut off.
The fuel-air mixture then passes
through the idle down channel and
is transferred to the idle channel in
the throttle body. The fuel-air
mix-
ture passes down the idle channel,
past the progression holes, to the idle
valve.
The
amount of
mixture
to
be
discharged is determined by the
position of the idle needle valve in
relation to its seat
in
the throttle
body.
During off-idle operation, when the
throttle valve is moved past the
idle
progression holes, each hole begins
discharging fuel as it is exposed to
the lower air
pressure
(manifold
vacuum>.
Continued opening of the
throttle valve
increases
engine R.P.M.
and air ftow through the
carburettor.
The greater air ftow through the
venturi causes a pressure drop in the
venturi great enough to bring the
main metering system into operation
as
the
idle fuel metering system
tapers
o.
f
f.
MAIN FUEL METERING SYSTEM
The main fuel metering system
(Fig.
4
>
supplies the fuel required
during the cruise or part-throttle
range. The system begins to func-
tion
when
the air ftow through the
carburettor venturi creates sufficient
vacuum to start fuel flowing in the
main
system.
The vacuum at the
tip of the main discha-rge jet will
increase as the
air
flow increases.
The faster the engine operates, the
more fuel will flow through the
main fuel system.
Fuel entering the main metering
jet, located at the base of the in-
clined main
channel,
ftows upwards
to the main discharge
jet.
Air from
the calibrated high-speed bleed ftows
down the high-speed bleed channel
and enters the main channel. The
air passes through holes spaced along
the body of the main discharge jet,
mixing with the fuel passing up the
main channel. The fuel and air
mix-
ture being lighter than solid
fuel,
responds faster to changes in ven-
turi pressures. The mixture ftows to
the tip of
the
main discharge jet
to be discharged into the filtered air
moving past and through the small
venturi.
ACCELERATING PUMP SYSTEM
Smooth
acceleration
requires
a
momentary increase in the supply of
.
needle valve. The progression holes
act as additional air bleeds at normal
idle.
The fuel-air mixture ftows past
the idle needle valve and seat and is
discharged through the idle discharge
nozzle located below the throttle
FIG. 3-Fuel Inlet System
Typical
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