2004 Yamaha YZ250F

2004 Yamaha YZ250F: New 48 mm Forks and Another Round of Refinement

The 2004 Yamaha YZ250F was an evolutionary update rather than an all-new generation, but Yamaha made several worthwhile improvements to a motorcycle that was already helping redefine the 250-class motocross landscape. The basic 249 cc five-valve engine, steel semi-double-cradle frame and overall geometry remained familiar from the 2003 machine, while attention turned to suspension performance, weight reduction and small engine refinements.

The most significant change was the move to a new 48 mm Kayaba inverted fork. This replaced the previous 46 mm design and incorporated a hydraulic bottoming system intended to reduce harsh metal-to-metal impact during hard landings. Front wheel travel remained 300 mm, while the Monocross rear suspension continued to provide 315 mm of wheel travel. Owners servicing the original front end can refer to the MXOwners fork oil reference for additional fork setup information.

The engine retained its 77.0 x 53.6 mm bore and stroke, 12.5:1 compression ratio and Keihin FCR-MX37 carburettor, but Yamaha reduced internal pumping losses and revised several components to improve response and durability. A titanium exhaust header replaced the previous steel item, while lighter frame details and titanium footpegs contributed to an overall weight reduction. The 2004 bike also retained the automatic decompression system introduced the previous year, making starting considerably easier than on the original 2001-2002 models.

For owners today, correct carburettor setup remains particularly important. The FCR can deliver excellent throttle response when properly jetted and maintained, but worn accelerator-pump components, incorrect float height or blocked passages can make starting and low-speed response difficult. Replacement and tuning possibilities can be checked through the MXOwners carburettor reference.

Mechanically, the 2004 model still uses a shared dry-sump oil supply for both engine and transmission rather than separate gearbox oil. Oil capacity is 1.0 litre for a normal change, 1.1 litres with filter replacement and 1.2 litres total. Frequent oil changes, clean air filtration and regular valve-clearance checks remain important on any early high-revving YZ250F.

The standard wheel combination remained 21 inches at the front and 19 inches at the rear, using 80/100-21 and 100/90-19 tyres. Owners replacing the originals can compare sizing information through the MXOwners Tyre Size Guide. When restoring a 2004 bike, model-year-specific suspension and chassis components are also worth checking carefully through the MXOwners Parts Finder, particularly because the new 48 mm fork distinguishes this model from the earlier 2001-2003 machines.