Yamaha YZ250(P)/LC, Owner'S Service Manual

Page: 530 / 584

7-3
SETTING
TUN
EC714032
Effects of setting parts in relation to throt-
tle valve opening
NOTE:
The power jet closes at 8,500 rpm of the engine,
after which only the main jet dominates.
1
Throttle valve opening
2
Full-open
3
Full-closed
EC715002
Main jet adjustment
The richness of air-fuel mixture with 3/4~4/4
throttle can be set by changing the main jet
1
.
*For EUROPE
1. Spark plug is too hot.
Select a main jet having higher calibrating
No. than standard. (To be enriched)
2. Spark plug is wet.
Select a main jet having lower calibrating No.
than standard. (To be leaned out)
Standard main jet
#178
*#175
EC71V000
Powet jet adjustment
The richness of air-fuel mixture under 8,500 rpm
to the extent of 1/2 to full opened throttle can be
set by changing the power jet
1
. A larger size jet
results in a richer mixture, and a smaller size in a
leaner mixture.
Standard Power jet #50
Setting part
Throttle valve opening
Full-closed 1/4 1/2 3/4 Full-open
Pilot jet
Pilot air screw
Diameter of
straight portion
Clip position
Throttle valve
Power jet
Main jet
Jet needle
5NX-9-30-7 6/5/01 4:47 PM Page 6