2010 Kawasaki KX450F, KX250F: progress through evolution

The Kawasaki KX450F, fitted with fuel-injection and a kickstart, only debuted last year, but its already being improved with more power, more durability and more rideability. The big upgrade is the first mass-production use of a bridged-box bottom piston, allowing for more power at high and over-rev engine speeds.
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