Yamaha VK540EF Service Manual page 49

CARBURETOR TUNING
ESS00066
Mid-range and high speed tuning
Adjustments are normally not required, but may
sometimes be necessary, depending on tem-
peratures, 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 intake
silencer 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 en-
gine.
2. Remove:
S Spark plugs
3. Check:
S 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.
ESS00087
High altitude tuning
Use the chart in CHAPTER 8 to select main jets
according to variations in elevation and temper-
ature.
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
3 Pilot screw
2-32
INSP
ADJ