Yamaha WR250F(N), Owner'S Service Manual

Page: 644 / 686

7 - 6
T U N
SETTING
Effects of adjusting the pilot jet (reference)
Å
Idle
ı
Fully open
1/4 1/2 3/4
+5%
–5%
#45
#40
#42
Å ı
Jet needle groove position adjustment
Adjusting the jet needle 1 position affects the
acceleration when the throttle is 1/8 to 3/4
open.
1. Too rich at intermediate speeds
Rough engine operation is felt and the
engine will not pick up speed smoothly. In
this case, step up the jet needle clip by
one groove and move down the needle to
lean out the mixture.
2. Too lean at intermediate speeds
The engine breathes hard and will not
pick up speed quickly.
Step down the jet needle clip by one
groove and move up the needle to enrich
the mixture.
* For EUROPE
** For CDN, ZA, AUS and NZ
NOTE:
It is recommended that in the summer the clip
position be changed from the 4th (STD) to the
2nd groove for a leaner air-fuel mixture. (For
AUS and NZ only)
Effects of changing the jet needle groove
position (reference)
Å
Idle
ı
Fully open
1 No.4 groove
2 No.2 groove
3
No.3 groove
Standard clip position
No.3 groove
*
,
** No. 4 groove
1/4 1/2 3/4
+10%
–10%
1
2
3
ı Å