Yamaha TZ250M1 Owner's Service Manual page 269

SETTING
EC71F002
Carburetor settings by correction coeffi-
cient
Now you should be able to understand the
essentials of basic carburetor setting from an
explanation given under "Basic process of car-
buretor setting" (P7-2).
Next is an explanation of how to select a main
jet to deal with changes in weather conditions
by means of a correction coefficient.
NOTE:
• Before this correction coefficient can be used,
satisfactory carburetor setting must have
been made.
• This correction coefficient can not be used if
there is a change in specification (e.g., igni-
tion timing, compression ratio, etc.).
Illustration:
Suppose the best setting was represented by a
#450 main jet at an air pressure of 1013 hPa
(760 mmHg) and an air temperature of 20°C
(68°F) in the previous riding.
In this riding, there has been a substantial
change in conditions; namely, an air pressure
of 1007 hPa (755 mmHg) and an air tempera-
ture of 30°C (86°F).
1. Refer to a table of correction coefficients
(P7-6) to find the correction coefficient for
the previous riding.
The correction coefficient A=100.0
2. Find the correction coefficient for this time.
The correction coefficient B=96.1
3. Use the following equation to calculate the
% size of a main jet needed in this particular
case.
Previous main jet size X X B/A
= Currently required main jet size
450 X 96.1/100 = 432.5
Thus, a #430 main jet can be selected.
7-5
TUN