Yamaha YZ125 2022, Owner'S Service Manual, Page: 267 / 278

ENGINE
10-8
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 ±30, 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
BR9EVX
(resistance type)