Yamaha RS90NL Supplément Au Manuel De D'atelier page 32

CARBURETOR TUNING
3. Check:
• Spark plug insulator 1 color
A medium to light tan color indicates normal
conditions.
Distinctly different color → Replace the main
jet.
4. The main jet should be adjusted on the basis of
the "Main jet selection chart".
NOTE:
By checking the condition of the spark plugs, it is
easy to get some idea of the condition of the
engine. This may diagnose potential problems
before engine damage occurs.
High altitude tuning
Use the chart in CHAPTER 9 to select main jets
according to variations in elevation and tempera-
ture.
NOTE:
These jetting specifications are subject to change.
Consult the latest technical information from
Yamaha to be sure you have the most up-to-date
jetting specifications.
1 Main jet
2 Pilot jet
8
INSP
ADJ