Yamaha YZ250 combustion chambers

Chamber selection:

1999-2022

Y20 - 22cc Stock compression for the X model 

Y21 - 21.1cc Stock (95+ octane)

Y22 - 20.1cc (100+ octane)

Y23 - 19.1cc (105+ octane)

1999-2022 big bore chambers:

YZ295 - 72mm 95+ octane

YZ296 72mm 100+ octane

1988-1998

Y31 - Stock
Y32 -  (95+ octane)
Y33 -  (100+ octane)