Yamaha VK540EF, Service Manual, Page: 112 / 439

2-36
CARBURETOR TUNING
INSP
ADJ
ESS00091
Troubleshooting
Trouble Diagnosis Adjustment
Hard starting Insufficient fuel Add gasoline.
Excessive use of
the starter or
choke Return the starter lever to its seated position so
that the starter valve is fully closed.
Fuel passage is
clogged or frozen Check and, if necessary, clean the fuel tank air
vent, the fuel filter and all of the fuel passages.
Check and, if necessary, clean the carburetor
air vents, fuel passages and the float valve.
Clean the float chamber of any ice or water.
Overflow Adjust the fuel level.
Poor idling:
Poor performance
Improper idling
speed adjustment Adjust the engine idle speed.
Refer to “Low speed tuning”.
at low speeds
Poor acceleration
Sl
t
Damaged pilot
screw Replace the pilot screw.
Slow response to
throttle
Engine tends to
Clogged bypass
hole Clean the bypass hole.
Engine tends to
stall
Clogged or loose
pilot jet Remove the pilot jet, clean it with compressed
air and then install it.
Make sure that the pilot jet is fully tightened.
Air leaking into the
carburetor joint Retighten the clamp screws on the carburetor
joints.
Defective starter
valve seat Clean or replace the starter valve seat.
Overflow Adjust the fuel level.
Poor performance
at mid-range
speeds:
Momentary slow
response to
Clogged or loose
pilot jet Remove the pilot jet, clean it with compressed
air, and then install it.
Make sure that the pilot jet is fully tightened.
res onse to
the throttle
Poor acceleration
Lean mixture Overhaul the carburetors.
Poor performance Clogged air vent Remove the air vent hose and clean it.
at normal speeds:
Excessive fuel
consumption
Poor acceleration
Clogged or loose
main jet Remove the main jet, clean it with compressed
air, and then install it.
Make sure that the main jet is fully tightened.
Poor acceleration
Overflow Check and, if necessary, clean the float and
float valve.