Yamaha VK540EF, Service Manual, Page: 113 / 439

CARBURETOR TUNING
INSP
ADJ
2-37
Trouble Diagnosis Adjustment
Poor performance
at high speeds: Starter valve is left
open Return the starter lever to its seated position so
that the starter valve is fully closed.
Power loss
Poor acceleration
Clogged air vent Remove and clean the air vent.
Poor acceleration
Clogged or loose
main air jet Remove the main jet, clean it with compressed
air, and then install it.
Make sure that the main jet is fully tightened.
Clogged fuel line Clean or replace the fuel line.
Dirty fuel tank Clean the fuel tank.
Air leaks into the
fuel line Tighten or replace the fuel line joint.
Low fuel pump
performance Repair or replace the fuel pump.
Clogged fuel filter Replace the fuel filter.
Clogged intake Remove any obstructions (e.g., ice).
Abnormal Lean mixture Clean and adjust the carburetors.
combustion:
Backfiring
Dirty carburetors Clean the carburetors.
Backfiring
Dirty or clogged
fuel line Clean or replace the fuel line.
Overflow: Clogged air vent Clean the air vent.
Poor idling
Poor performance
at lo
mid range
Clogged float
valve Disassemble and clean the float valve.
Do not scratch the valve seat.
at low, mid-range,
and high speeds
Excessive fuel
consumption
Hard starting
Scratched or
unevenly worn
float
valve or valve seat Clean or replace the float valve and valve seat.
The valve seat and body must be replaced
as a set.
Hard starting
Power loss
Broken float Replace the float.
Power loss
Poor acceleration
Incorrect float
level Check and, if necessary, replace the following
parts:
Float tang
Float (entire assembly)
Arm pin