Yamaha VK540EF Service Manual page 108

CARBURETOR TUNING
ESS00089
Low speed tuning
The carburetors are built so that low speed tun-
ing can be done by adjusting the pilot screw 1
and throttle stop screw 2 .
CAUTION:
Never run the engine without the air intake
silencer installed. Severe engine damage
may result.
1. Tighten the pilot screw until it is lightly seated
and then back it out the specified number of
turns.
Pilot screw 1 :
1-1/4 turns out
Pilot screw effects:
Turn in
Leaner
Mixture
2. Set the engine idle speed by turning the
throttle stop screw 2 in (to increase engine
speed) or out (to decrease engine speed).
Standard idle speed:
1,200
3. If low-speed performance is still poor at high-
er elevations under extreme conditions, the
standard pilot jets may need to be replaced.
In this way, the proper air/fuel mixture is ob-
tained.
NOTE:
In this case, use a larger numbered pilot jet to
enrich the air/fuel mixture.
Standard pilot jet:
#90
2-34
INSP
ADJ
STD setting Turn out
Richer
Mixture
100 r/min