Yamaha YZ250/LC Manuel Du Propriétaire page 526

Table des Matières

Carburetor setting

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

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).

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

taking 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.

Atmospheric conditions and carburetor

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).