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14-34
CARBURETOR-BBD
1
' / 2
INCH
STEP-UP R O D S
M U S T M O V E
FREELY
N K 6 1 7
AD L O A D STEP
NTERMEDIATE
MIXTURE STEP
W
fig. 7-Step-up
Rods Free
Play
the plunger and press downward. No fuel should be
emitted from either the intake or discharge passage,
as shown in (Fig. 6).
If any fuel does emit from either passage, it indi-
cates the presence of dirt or a damaged check ball
seat. Check the passage again and repeat test. If leak-
age is still evident, install a new check ball. The
fuel inlet check ball is located at the bottom of the
plunger well.
( 5 )
Install new gaskets on the venturi cluster, and
install in position in the main body. Install the cluster
screws and tighten securely. Test pump discharge by
pressing pump plunger down. Two fine streams of
fuel should be forced from the cluster. If either stream
is restricted or diverted, remove cluster and reclean.
After test, pour the fuel from the bowl and remove
pump plunger.
(6) Install the main metering jets. Tighten secure-
ly. Refer to (Fig. 3).
(7) Before installing the step-up piston, be sure the
step-up rods are able to move freely, each side of the
vertical position, as shown in (Fig. 7). The step-up
rods must be straight, smooth and free to move for-
ward and backward from vertical.
( 8 )
Slide the step-up piston gasket down into
posi-
tion in the piston well, then install the step-up piston
spring, step-up piston and rods. Carefully guide the
step-up rods into the main metering jets (Fig.
2).
Install the retaining screw and tighten securely. Check
piston for free operation in the well.
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 rubber-tipped
fuel inlet needle. The rubber tip is flexible enough to
make a good seal on the needle seat, and to give in-
creased resistance to flooding.
FINGER PRESSING
A G A I N S T FULCRUM
P I N RETAINER
. .
'
NK618
Fig. 8-Measuring
the
float Setting
The
use
of the rubber-tipped needle requires a new
procedure in adjusting the float setting. Care should
be taken to perform this operation accurately in order
to secure the best performance and fuel economy.
(1) To correctly set the float height when the car-
buretor
is
being overhauled, install the floats with the
fulcrum pin and pin retainer in the main body.
(2)
Install the rubber-tipped needle, seat and gasket
in the body and tigten securely.
(3) Invert the main body
so
that the weight of
the float only is forcing the needle against the seat.
Hold finger against the retainer to fully seat the ful-
crum pin.
(4)
Using Tool T109-280 or a "T" scale, measure the
float, as shown in (Fig. 8). There should be
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
inch setting
again and repeat the lip bending operation as re-
quired.
CAUTION: When bending the float lip, do not al-
low the lip to push against the needle as the ryn-
thetic rubber tip can
be compressed sufficiently to
cause a false setting which will affect correct level
of fuel in the bowl.
After being compressed, the tip is very slow to re-
cover
its
original shape.
CAUTION: It
i s
very important that the float lip
k
perpendicular to the needle or slanted not more
than ten degrees away from the needle when the
float height
is
correct.
Air Horn
(1)
Test the freeness of the choke mechanism in
the air horn. The choke shaft must float free to op-
erate correctly. If the choke shaft sticks in the bearing
areas, or appears to be gummed from deposits in the
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