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ZENITH 68-7 SERIES CARBURETOR
Wisconsin Motor Corporation Part No. L-63 Series
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. This design
makes them particularly adaptable to smaller farm tractors and a
great variety of agricultural machines and industrial units.
Fuel supply system, Fig. 1, is made up of the threaded fuel inlet,
the fuel valve seat, fuel valve needle, float and fuel bowl.
The fuel supply line is connected to the threaded inlet. The fuel
travels through the fuel valve seat and passes around the fuel
valve and into the fuel bowl. Te level of fuel in the fuel
chamber is 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 according to its speed and load.
The inside bowl vent as illustrated by the passage originating in
the air intake and continuing through to the fuel bowl, is a method
of venting the fuel bowl to maintain proper fuel mixtures even
though the air cleaner may become restricted. This balancing is
frequently referred to as an "inside bowl vent".
Idle system, Fig. 2, consists of two idle discharge holes, idle
air passage, idle adjusting needle, idle jet, and fuel pick-up
passage.
The fuel for idle is supplied through the main jet to a well direct-
ly below the main discharge jet. The pick-up passage is connect-
ed to this well by a restricted drilling at the bottom of this pas-
sage. The fuel travels through this channel to the idle jet cali-
bration. The air for the idle mixture originates back of (or from
behind) the main venturi. The position of the idle adjusting nee-
dle in this passage controls the suction on the idle jet and there-
by the idle mixture. Turning the needle in closer to its seat re-
sults in a greater suction with a smaller amount of air and there-
fore 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.
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 jet, 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 the part throttle
range from about one-quarter to full throttle opening. To maintain
a proper mixture ratio a small amount of air is admitted through
the well vent into the discharge jet through the air bleed holes in
the discharge jet at a point below the level of fuel in the meter-
ing well.
The passage of fuel through the high speed system is not a com-
plicated process. The fuel flows from the fuel chamber through
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 system, Fig. 4, consists of a valve mounted on a shaft
1
L-63 Series
MI-7-17
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