Yamaha RS90NL, Suplementary Service Manual

Page: 36 / 308

10
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 throttle stop screw
1 .
CAUTION:
Never run the engine without the air filter case
installed. Severe engine damage may result.
1. Set the engine idle speed by turning the throttle
stop screw
1
in (to increase engine speed) or
out (to decrease engine speed).
2. If low-speed performance is still poor at higher
elevations under extreme conditions, the stan-
dard pilot jets may need to be replaced. In this
way, the proper air/fuel mixture is obtained.
NOTE:
In this case, use a larger numbered pilot jet to
enrich the air/fuel mixture.
Standard pilot jet:
#45
Engine idle speed:
1,300 ~ 1,500 r/min