Yamaha VK540EF Service Manual page 110

ESS00090
Main jet selection chart
Spark plug color
Light tan or gray
Dry black or fluffy
deposits
White or light gray
White or gray
insulator with small
black or grayish
brown spots and
electrodes having
a bluish-burnt
appearance
Melted electrodes
and possible a
blistered insulator
Metallic deposits on
insulator
CARBURETOR TUNING
Main jet selection chart
Diagnosis
Carburetors are
tuned properly.
Mixture is too rich.
Mixture is too lean.
Mixture is too lean.
The piston is
damaged or seized.
Mixture is too lean.
The spark plug
melted.
2-35
Remedy
Replace the main jet with the next smaller
size.
Replace the main jet with the next larger
size.
Replace the piston and spark plug.
Tune the carburetors again. Begin with
low-speed tuning.
Check the piston for holes or seizure.
Check the cooling system, gasoline octane
rating and ignition timing. After replacing
the spark plug with a colder type, tune the
carburetors again. Begin with low-speed
tuning.
INSP
ADJ