Yamaha RS90K Manuel D'atelier page 162

CARBURETOR TUNING
Engine idle speed:
1,300 ~ 1,500 r/min
3. 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
2-59
INSP
ADJ