THROTTLE
Ir\
r;
..
VAPORIZE
-.GASOLINE
*NOTE: VENT
EXTENDS THROUGH
METERING
ydL
WELL
LATER
MODELS
IDLE ]ET OPERATING
IDLE TRANSFER
WELL VENT
MAIN JET OPERATING
FIGURE
22.
CARBURETOR CIRCUITS
PRIOR
TO
SPEC
R
section of the carburetor throat). This pressure drop
operates the load circuit drawing fuel up the main
nozzle where it mixes with air at the nozzle opening.
The main adjusting needle controls fuel delivery.
As the throttle opens, the manifold vacuum decreases
so
the idle circuit becomes less effective.
In
a certain
range, the two circuits blend, both delivering fuel, but
as load is increased, the load circuit takes over.
With the load circuit in operation, as the load is
increased, the throttle opens to deliver more fuel. The
main nozzle won't immediately deliver this increased
fuel because of the jets controlled by the adjusting
needle. To prevent lag when load is increased, a
metering well around the outside of the nozzle
delivers fuel until the main jet can catch up with the
increased demand.
Adjustment, Electric Choke:
Under normal operation,
adjust the choke
so
the distance measured between
the choke and carburetor throat (Figure
18)
is as
shown in the table with the engine cold. Use the
straight shank end of a drill bit to measure the gap.
The upturned air cleaner must be removed for choke
adjustment. To adjust the choke, loosen the two
screws on the cover plate and rotate the cover
assem bly.
Forcing the needle against its seat will
bend the needle. The needle does not
shut off fuel completely when turned all the way in.
Adjustment, With
Load:
The carburetor should be
adjusted
in
2
steps
-
first the idle adjustment and
then the load adjustment. See Figure
23.
If
the Carburetor is completely out of adjustment
so
the engine
won't run, open both needle valves
1
to
1-1/2
turns off theirseats to
permit starting. Don't force the needle valves against their seats.
This will damage the needle.
THROTTLE
STOP SCREW
r
MAIN FUEL
AD JUSTMEM
ADJUSTMENT
THIS DISTANCE
INCH AT NO LOAD
PRIOR TO SPEC
R
MAIN FUEL
ADJUSTMENT
ml
A
DISTANCE
AT NO LOAD
BEGIN
SPEG
R
I
NYLON ROD EXTENDING
DOWN THROUGH LOWER
SHROUD PAN
FIGURE
23.
ADJUSTING GASOLINE CARBURETOR
Before adjusting the carburetor, be sure the ignition
system is working properly and the governor is
adjusted. Then allow the engine to warm up.
1.
With no engine load, turn idle adjustment out until
engine speed drops slightly below normal. Then
turn needle in until speed returns to normal.
2.
Apply a full load to engine. Carefully turn main
adjustment in until speed drops slightly below
normal. Then turn needle out until speed returns
to normal.
23
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