Yamaha YZ250X 2023, Owner'S Manual

Page: 134 / 146

ENGINE
8-9
EAM30603
CHANGE OF THE HEAT RANGE OF SPARK
PLUGS
Judging from the discoloration of spark plugs, if
they are found improper, it can be corrected by
the following two methods; changing carburetor
settings and changing the heat range of spark
plug.
•
In principle, it is advisable to first use spark
plugs of standard heat range, and judging from
the discoloration of spark plugs, adjust carbu-
retor settings.
•
If the calibration No. of the main jet must be
changed by ±15, it is advisable to change the
heat range of spark plugs and newly select the
proper main jet.
TIP
• When checking the discoloration of spark
plugs, be sure to stop the engine immediately
after a run and check.
•
Avoid racing.
• When changing the heat range of spark plugs,
never attempt to change it more than ±1 rank.
• When using a spark plug other than standard,
check its heat range against the standard and
check that it is a resistance type.
•
Note that even if the discoloration seems prop-
er, it may slightly vary with the spark plug mak-
er and oil in use.
Standard spark plug
BR8EG
(resistance type)