Tuning; Carburetor Setting; Atmospheric Conditions And Carburetor Setting - Yamaha YZ250(V) Owner's Service Manual

SETTING
EC700000

TUNING

EC710000
ENGINE
EC711001

Carburetor setting

9 The role of fuel is to cool the engine, and in the
case of a 2-stroke engine, to lubricate the
engine in addition to power generation. Accord-
ingly, if a mixture of air and fuel is too lean,
abnormal combustion will occur, and engine
seizure may result. If the mixture is too rich,
spark plugs will get wet with oil, thus making it
impossible to bring the engine into full play or if
the worst comes to the worst, the engine may
stall.
9 The richness of the air-fuel mixture required for
the engine will vary with atmospheric conditions
of the day and therefore, the settings of the car-
buretor must be properly suited to the atmos-
pheric conditions (air pressure, humidity and
temperature).
9 Finally, the rider himself must make a test-run
and check his machine for conditions (pick-up of
engine speed, road surface conditions) and for
the discoloration of the spark plug(s). After tak-
ing these into consideration, he must select the
best possible carburetor settings.
It is advisable to make a note of settings,
atmospheric conditions, road surface condition,
lap-time, etc. so that the memorandum can be
used as a reference useful for future.
EC712000
Atmospheric conditions and carburetor
setting
Air temp. Humidity
High High
Low Low
The reason for the above tendency is that the
richness or leanness of a fuel mixture depends
on the density of the air (i.e. the concentration of
oxygen in it).
7-1
TUN
Air
pressure Mixture Setting
(altitude)
Low
Richer Leaner
(high)
High
Leaner Richer
(low)