Sudco Vol 38

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Carburetor Tuning
530
Jetting Your Slide Valve Carburetors
All Keihin carburetors are pre-jetted for bolt-on
operation. Carburetors are jetted using stock
motorcycles and watercrafts. Any major engine
modiications like higher compression pistons
and racing exhaust systems may require minor
jetting adjustments. The followong is a guideline
jetting in the order given below.
1) CORRECT FLOAT HEIGHT
Before changing any jetting parts, check the
carburetor loats for correct height. Measure
the height from the bottom of the loat to the
carburetor-body gasket surface. Correct
height can be found on the chart. When
checking the loat height, the loat should be
resting, but not depressing, the spring
loaded loat valve pin. This can be done by
tilting the carburetor until the loat tab just
makes contact with the valve pin. If
adjustment is needed, bend the metal tab on
the loat arm until correct height is
obtained. ----- see example #1.
2) IDLE
Set idle speed to proper r.p.m. by adjusting
the IDLE SPEED SCREW. Turn the IDLE
MIXTURE SCREW or the AIR SCREW to
achieve highest speed and best response.
The IDLE MIXTURE SCREW (FCR) controls
fuel delivery to the idle port and the SCREW
is located on the engine side of the
carburetor slide. Turning the IDLE
MIXTURE SCREW out will male idle and
off-idle richer. Turning IDLE MIXTURE
SCREW (CR, PWK, PJ, PE) controls the
amount of air to the IDLE and SLOW
CIRCUIT. The SCREW is located on the air
cleaner side of the throttle slide and turning
the SCREW out will lean the mixture and
turning the SCREW in (clockwise) will
richen mixture.
3) OFF IDLE TO 1/4 THROTTLE
The SLOW JET and SLOW AIR JET are most
effective in this range, use a larger
SLOW JET or a smaller SLOW AIR JET. The
opposite holds true for a leaner mixture.
Calibration Chart ( )for FCR, CRS,
PWK, PJ, PE
Float Height
NOTE: (See Jetting instruction #1)
for correct procedure.
IDLE 1/8 1/4 1/2 3/4 W.O.T.
Effectiveness
PJ PWM PE
ALL 38 24-38 30-34 36-39
16mm 6.5mm 20mm 22.25mm
FCR CR PWK PD PD
ALL ALL 28 35-39 26-30 36-39
9mm 14mm 19mm 16mm 12.5mm 22.5mm