Yamaha TZ250M1 Owner's Service Manual page 271

SETTING
EC71H040
Other setting parts
1. Power jet 1
Power jet is not basically changed. Since
the areas of the main jet and main nozzle
overlap each other, special knowledge is
w
required for a setting change.
A larger size results in a richer mixture and
a smaller size in a leaner mixture.
Factory-set power jet
2. Pilot jet 1
The pilot jet is used in relation to the engine
response at small throttle opening. This is
changed when the main nozzle setting is
w
not enough.
A larger size results in a richer mixture and
a smaller size in a leaner mixture.
Factory-set pilot jet
3. Pilot air screw 1
The pilot air screw relates to the engine
response at a smaller opening than for the
pilot jet.
w
This setting may be changed for want of
time or in emergency, but it is basically set
at the factory-set pilot air screw position.
Factory-set pilot air
screw position
4. Spark plug
The spark plug heat range is not basically
changed.
Constant attention to the discoloration of
w
the spark plug and piston head will enable
you to tell to some extent whether the set-
ting is good or bad.
Standard spark plug
NOTE:
For the effects each setting part has, refer to
"Effects of setting parts in relation to throttle
valve opening" (P7-2).
7-7
TUN
#55
#30
1-1/2 turns out
R6179A-105P/NGK