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CARBURETOR TUNING
Mid-range and high speed tuning
Adjustments are normally not required, but
may sometimes be necessary, depending on
temperatures, altitude or both.
Mid-range speed and high speed tuning (from
1/4 to full-throttle) can be done by adjusting
the main jet.
CAUTION:
Never run the engine without the air filter
case installed. Severe engine damage may
result.
1. Start the engine and operate the machine
under normal conditions to make sure that
the engine operates smoothly. Stop the
engine.
2. Remove:
• Spark plugs
3. Check:
• Spark plug insulator
A medium to light tan color indicates nor-
mal 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:
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
temperature.
NOTE:
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.
Main jet
Pilot jet
12
INSP
ADJ
color
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