That may come as a surprise to some, if only because Yamaha didn't actually make its first proper dirt bike until the late 1960s. That era saw Yamaha's design team release a few signature off ...
XEMX makes two separate conversion kits (the air-cooled XE2 and liquid-cooled XE4) for Yamaha's YZ250F and YZ450F dirt bikes, but the brand is currently only accepting pre-orders for the XE4 model.
Yamaha points to "the push for more environmentally friendly machines" as the impetus for 4-stroke dirt bikes -- which sounds ...