Zenith Model 68-7; Wisconsin L-63 Series - Wisconsin VH4D Repair Manual

CARBURETOR
ZENITH MODEL 68-7
WISCONSIN L-63 SERIES
L-63 Serles
The Zenith 68-7 Series carburetor is of an up-draft single venturi
design with a 1" S.A.E. barrel size and a 7/8" S.A.E. flange.
The carburetors are made with selective fuel inlet, and with or
without a main jet adjustment. These carburetors are ~balanced"
and "sealed", and the semi-concentric fuel bowl allows operation
to quite extreme angles without flooding or starving.
BOWL VENT
FUELINLET
FUEL VALVE
SEAT
FUEL VALVE
NEEDLE
FLOAT
needle in this passage controls the suction on the idle jet and
thereby the idle mixture. Turning the needle in closer to its seat
results in a greater suction with a smaller amount of air and
therefore a richer mixture. Turning the needle out away from its
seat increases the amount of air and reduces the suction, and a
leaner mixture is delivered. The fuel is atomized and mixed with
the air in the passage leading to the discharge holes and enters
the air stream at this point.
WELL VENT
VENTURI
MAIN JET
Fig. 1
Fuel supply system, Fig. 1, is made up of a threaded
fuel inlet,
fuel valve seat, fuel valve needle, float and fuel bowl. Fuel tra-
vels through the fuel valve seat and passes around the fuel valve
and into the fuel bowl. The level of the fuel in the fuel chamber
~s regulated by the float through its control of the fuel valve.
The fuel valve does not open and close alternately but assumes
an opening, regulated by the float, sufficient to maintain a proper
level in the fuel chamber equal to the demand of the engine ac-
cording to its speed and load.
The inside bowl vent as illustrated by the passage originating in
~he air intake and continuing through to the fuel bowl, is a method
of venting the fuel bow1 to maintain proper air fuel mixtures even
though the air cleaner may become restricted. This balancing is
frequently referred to as an "inside bowl vent".
IDLE DISCHARGE HOLES
IDLE
NEEDLE
E PLATE
(Idle Position)
IDLE AIR
IDLE JET
IDLE
PICK-UP
PASSAGE
Fig. 3
High speed system, Fig. 3, controls the fuel mixture at part throt-
tle speeds and at wide open throttle. This system consists of a
venturi, controlling the maximum volume of air admitted into the
engine; the main iet, which regulates the flow of fuel from the
float chamber to the main discharge jet; the well vent, which
maintains uniform mixture ratio under changing suction and en-
gine speeds; and a main discharge jet, which delivers the fuel
into the air stream.
The main jet controls the fuel delivery during part throttle range
from about one-quarter to full throttle opening. To maintain a
proper mixture, a small amount of air is admitted through the well
vent into the discharge jet through air bleed holes in the dis-
charge jet at a point below the level of fuel in the metering well.
The passage of fuel through the high speed system is not a com-
plicated process. The fuel flows from the fuel chamber thrbugh
the main jet and into the main discharge jet where it is mixed
with air admitted by the well vent, and the air-fuel mixture is
then discharged into the air stream of the carburetor.
CHOKE
(Open Position)
Fig. 2
Idle system, Fig. 2, consists of two idle discharge holes, idle
¯ ir passage, idle adjusting needle, idle jet, and fuel pick-up
passage. The fuel for idle is supplied through the main jet to a
well directly below the main discharge jet. The pick-up passage
is connected to this well by a restricted drilling at the bottom of
this passage. The fuel travels through this channel to the idle
jet calibration. The air for the idle mixture originates back of (or
from behind) the main venturi. The position of the idle adjusting
36
Fig. 4
Choke system, Fig. 4, consists of a valve mounted on a shaft
located in the aiz entrance and operated externally by a lever
mounted on the shaft. The choke valve is used to restrict the air
entering the carburetor. This increases the suction on the jets