Yamaha RS90K, Service Manual

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2-58
INSP
ADJ
CARBURETOR TUNING
A
Standard main jet
B
Main jet whose diameter is 10% smaller than stan-
dard
C
Main jet whose diameter is 10% larger than standard
CAUTION:
If the air filter case is removed from the carbu-
retors, the change in pressure in the intake will
create a lean mixture that may cause severe
engine damage. The air filter case has no effect
on performance characteristics and must be
secured to the carburetors during carburetor
tuning and adjustment. Also, it must always be
in place when the engine is operated. Regularly
clean the air filter and keep it free from obstruc-
tions.
Low-speed tuning
The carburetors are built so that low speed tuning
can be done by adjusting the pilot screw
1 and
throttle stop screw
2
.
CAUTION:
Never run the engine without the air filter case
installed. Severe engine damage may result.
1. Tighten the pilot screw until it is lightly seated
and then back it out the specified number of
turns.
Pilot screw
1
:
2 turns out
NOTE:
Number of return rotation of pilot screw may vary
depending on each cylinder.
Make sure to rotate the screw backward after listing
its present number of return rotation on each cylin-
der.
Pilot screw effects:
2. Set the engine idle speed by turning the throttle
stop screw
2
in (to increase engine speed) or
out (to decrease engine speed).
Turn in STD setting Turn out
Leaner
Mixture
Richer
Mixture
1
2