The KFX® 400 is powered by a 398cc, liquid-cooled, four-stroke engine featuring double overhead cams and four valves atop a chrome composite-plated aluminum alloy cylinder. Fed by a new 37mm high-performance carburetor, it includes electric start and has a counter balancer to reduce vibration.

The KFX® 400 engine utilizes a "dry sump" design, with the engine oil being carried in the tubes of the high-performance chassis instead of the traditional location beneath the engine. This design enabled engineers to shorten overall engine height so it can be placed lower in the chassis for enhanced stability while providing higher ground clearance.

Transmitting power from the engine to the rear wheels is a high-performance five-speed-plus-reverse manual transmission and efficient O-ring chain.

A high-performance powerband requires an equally advanced chassis, so the KFX® 400 ATV engine rides in a high-tensile steel frame and subframe. Suspension duties are handled by dual front A-arms with new fully adjustable shocks that provide 8.5 inches of travel, while an aluminum-alloy swingarm with fully adjustable shock provides 9.1 inches of travel on the rear. Contributing to the KFX® 400's low, 373-pound dry weight are competition-inspired aluminum-alloy wheels, and stopping power is provided by dual front disc brakes and a single rear disc brake.