Yamaha TZ250M, Owner'S Service Manual

Page: 268 / 287

SETTING
7-4
If the main jet is fully adjusted with not much
allowance for discoloration, use a main jet
which is approximately #20 lager.
Run a few laps of the circuit to check the
engine for response to revolutions. Also
check for the discoloration of the spark
plug(s) and piston(s).
Use a main jet of a smaller size if good
response to engine revolutions is achieved
with an allowance for the discoloration of
the spark plug(s) and piston(s).
On the other hand, if the use of a different
main nozzle appears to produce less
power, change to a main nozzle of a larger
size.
Example:S-1
≥
S-2
Factory-set main nozzle S-4
w
NOTE:
Difference between individual riders or differ-
ence between circuit layouts greatly affect the
main nozzle setting.
1. Rider who frequently uses mid-open throttle
2. Circuit that requires frequent throttle open-
ing and closing
3. Wet environment
Conditions as mentioned above require a
longer period of throttle closing, resulting in the
drawn in mixture staying longer in the
crankcase. Such setting in turn will inevitably
cause the mixture to be richer at the next throt-
tle opening, a main nozzle of a smaller size
has to be used.
TUN