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CARBURETOR-BBD
1
' / 4
INCH
14-27
(Fig. 3). Install retaining screw and tighten securely.
A step-up piston stuck in the UP position will cause
a rich mixture at part throttle, whereas a piston stuck
in the
DOWN
position will cause a lean mixture at
wide open throttle and poor acceleration.
Measuring the Float Setting
The carburetors are equipped with a synthetic rub-
ber tipped fuel inlet needle. The needle tip is a rub-
ber material which is not affected by gasoline and
is
stable over a wide range of temperatures. The tip is
flexible enough to make a good seal on the needle
seat, and to give increased resistance to flooding.
The use of the new inlet needle requires a new pro-
cedure in adjusting the float setting. Care should be
taken to perform this accurately in order to secure the
best performance and fuel economy.
To correctly set the float height, when the carbu-
retor is being overhauled, proceed as follows:
(1) Install the floats with the fulcrum pin and pin re-
tainer in the main body.
(2) Install the needle, seat and gasket in the body
and tighten securely.
(3) Invert the main body (catch the pump intake
check ball) so that the weight of the floats
only,
is forcing the needle against the seat. Hold finger
against retainer to fully seat the fulcrum pin.
(4)
Using Tool T109-282 or a "T" scale, check the
float, as shown in (Fig. 10). There should be ! A inch
from the surface of the fuel bowl to the crown of each
float at the center.
If an adjustment is necessary, hold the floats on
the bottom of the bowl and bend the float lip toward
or away from the needle. Recheck the
VI
inch set-
ting again then repeat the lip bending operation as
required.
CAUTION: When bending the float lip, do not allow
the lip to push against the needle
as
the syn-
thetic rubber tip can be compressed sufficiently to
cause a false setting which will affect correct level
of fuel in the bowl.
Fig. IO-Measuring
the
Float Setting
BOWL VENT VALVE
PLUNGER
SPRING SEAT
CLIP PFSITIONS
I
BOWL VENT VALVE
SPRING
OPERATING CLIP
NK688
Fig. 1 1-Accelerator
Pump Assembly
After being compressed, the tip is very slow to re-
cover its original shape.
It is very important that the float lip be perpendicu-
lar to the needle or slanted not more than ten de-
grees away from the needle when the float is
set
cor-
rectly.
Air Horn
(1) Assemble the pump plunger, spring and spring
seat, as shown in (Fig.
11).
Slide plunger shaft through
opening in air horn. Install bowl vent valve over
plunger shaft, then engage with pump rocker arm.
(2) Place a new gasket on the main body, then in-
stall the air horn. Refer to (Fig. 2). Install attaching
screws and tighten securely. (When installing air horn
be sure the leather on the plunger does not fold back).
(3) Engage the fast idle connector rod in the choke
lever and fast idle cam. Secure with hairpin clip.
(4)
Engage the accelerator pump operating rod in
the proper hole in the rocker arm (depending on car-
buretor) and in the center hole in the throttle lever.
Refer to (Fig.
1).
Install clips to secure.
Choke Vacuum Diaphragm
Inspect the diaphragm vacuum fitting to insure that
the passage is not plugged with foreign material. Leak
check the diaphragm to determine if it has internal
leaks. To do this, first depress the diaphragm stem,
then place a finger over the vacuum fitting to seal the
opening. Release the diaphragm stem. If the stem
moves more than
1 / 1 6
inch in 10 seconds, the leakage
is excessive and the assembly must be replaced.
Install the diaphragm assembly on the airhorn
as follows:
(1) Assemble to the airhorn and tighten the at-
taching screws securely.
(2) Install the choke operating link in position be-
tween the diaphragm plunger (stem) and the choke
lever. Install the clip to secure.
(3) Inspect the rubber hose for cracks before plac-
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