Yamaha YZ125(R)/LC, Owner'S Service Manual

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7-13
TUN
SETTING
EC71X000
Selecting the rotor
If you feel the engine pick up faster depending
on the course condition, you can control it by
changing the rotor to the one with a greater iner-
tial mass.
* Inertial mass: The inertial mass of the body is
proportional to its weight and increases in pro-
portion to the square of the distance between its
rotation center and center of gravity. For the
same weight, a greater distance from its rota-
tion center produces greater inertial mass.
Greater initial mass gives a feeling of greater
torque in response to engine revolutions but is
accompanied by greater pick up resistance.
Engine characteristics are shown below in rela-
tion to each rotor:
9
Standard rotor
Engine pickup is faster in the entire engine
speed range.
Pickup is fast at an extremely low engine
speed.
9
Optional rotor
A feeling of torque is obtained at high engine
speed.
A broader power band is felt from mid speed to
over revs.
NOTE:
9
Engine pick up differs according to the course
condition, rider, the settings, etc. Select a suit-
able rotor by comparing it with the standard
one in operation.
9 It is difficult to be advantageous under all
course conditions with a change in the rotor.
Measure the lap times in accordance with race
points and select a rotor to produce a good
entire balance.
Part name Part number *Inertial mass
1 1
Standard rotor 5CU-85550-11 0.0004kg•m 2
2 2
Optional rotor 5UN-85550-00 0.00045kg•m 2