The Honda 400EX is powered by a 397cc air-cooled, single-cylinder, four-stroke engine with a single overhead camshaft (SOHC).
Engine design and specs
Core characteristics
Key specs at a glance include displacement, configuration, cooling method, and the valve setup, which shape power delivery and durability.
- Displacement: 397cc
- Configuration: single-cylinder, four-stroke
- Cooling: air-cooled
- Valve train: single overhead camshaft (SOHC)
- Transmission: five-speed manual with a foot-operated clutch
- Fuel delivery: carbureted (not fuel-injected)
These features provide a simple, robust powerplant known for predictable performance and ease of maintenance in sport-quad use.
Production years and variations
Model timeline
The 400EX was produced across the late 1990s through the mid-to-late 2000s in most markets, with regional variations in availability and updates.
- Production span: roughly 1999–2008 in many markets; some regions saw earlier or later starts and ends.
- Replacement: Honda introduced the TRX450R in 2009, effectively succeeding the 400EX as Honda’s sport ATV flagship.
- Market and trim: the model offered various trims and updates over its run, reflecting Honda’s ongoing ATV refinements.
Despite its age, the 400EX remains a reference point for reliability and straightforward maintenance in the used-ATV community.
Summary
The Honda 400EX runs on a compact 397cc air-cooled, single-cylinder four-stroke engine with an SOHC configuration. Paired with a five-speed manual transmission and carbureted fuel delivery, this setup contributed to the model’s reputation for reliability and approachable performance in sport-quad riding.