Gravely Convertible 7.6 Service Manual page 8

part throttle range from about one-quarter to full throttle
opening. A main jet adjustment permits a limited control of the
main jet fuel. Oridinarily an adjustment of 1 1/2 turns from its
seat will give proper mixture. To maintain a proper mixture
ration 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 metering
well.
CHOKE SYSTEM
(See Figure 6)
At high speeds 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.
The choke system consists of a valve mounted on a shaft
located in the air 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
when starting the engine. The choke valve is of a
"Semi-Automatic" type, having a poppet valve incorporated in
its design, which is controlled by a spring.
The poppet valve opens automatically when the engine
starts and admits air to avoid over-choking or flooding of the
engine. The mixture required for starting is considerably richer
than that needed to develop power at normal temperatures. As
the engine fires and speed
Figure 5
Figure 6
and suction are increased, the mixture ratio must be
rapidly reduced. This change is accomplished through
adjustment of the choke valve and the automatic opening
of the poppet valve to admit more air when the engine
fires.
SEPARATE CARBURETOR BODIES
(a) Remove the four assembly screws using a screw
driver.
(b) Separate the throttle body from the fuel bowl
assembly.
DISASSEMBLE THROTTLE BODY
(a) Remove float axle as follows:
(1) Press screwdriver against float axle at slotted side of
float hinge bracket and force through hinge bracket.
(2) Remove float axle completely with fingers from
opposite side and remove float.
(b) Remove fuel valve needle.
(c) Remove the assembly gasket.
(d) Remove the fuel valve seat and fibre washer.
(e) Remove the idle jet using a small screwdriver.
(f) Remove the idle adjusting needle and friction spring.
DISASSEMBLE FUEL BOWL BODY
(a) Remove the main jet adjusting needle assembly and
fibre washer using a ½"
(b) Remove the drain plug (hex) from bottom of fuel
bowl.
(c) Remove main jet and fibre washer.
(d) Remove main discharge jet and fibre washer from center
of large opening in machined surface of the fuel bowl.
(e) Remove well vent jet from center of large opening in
machined surface of the fuel bowl with a small
screwdriver.
CLEANING PARTS
(a) Clean all metal parts thoroughly with cleaning solution
and rinse in solvent.
(b) Blow out all passages in the air intake and fuel bowl
casting and throttle body.
(c) NOTE: Be sure all carbon deposits have been removed
from throttle bore and idle discharge holes. It is advisable
to reverse flow of compressed air in all passages to insure
that all dirt has been removed. Never use a wire or drill to
clean out jets.
INSPECTION OF PARTS
(a) Float Assembly. Replace float assembly if loaded with
gasoline, damaged, or if float axle bearing is worn
excessively. Inspect top side of float lever for wear where
it contacts fuel valve needle.
NOTE: Such wear can affect the float level.
(b) Float Axle. Replace if any wear can be visually detected
on the bearing surface.
(e) Fuel Valve Seat and Needle Assembly. Always replace
fuel valve seat and needle because both parts wear and
may cause improper float level.
(d) Idling Adjustment Needle and Spring. Inspect point of
needle. This must be smooth and free of ridges.
(e) Gaskets. Replace all gaskets and fibre washers every time
the carburetor is disassembled.
REASSEMBLY
FUEL BOWL BODY
(a) Install main discharge jet and fibre washer in fuel bowl
and tighten firmly.
(b) Install well vent jet in fuel bowl and tighten with a small
screwdriver.
wrench.
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