2004 Yamaha YZ450F
General Specifications
| Model | Yamaha YZ450F |
| Year | 2004 |
| Category | Motocross |
| Engine Type | Liquid-cooled, 4-stroke, DOHC, 5-valve single-cylinder |
| Weight | Approximately 100.5 kg dry |
Engine
| Displacement | 449 cc |
| Bore x Stroke | 95.0 x 63.4 mm |
| Compression Ratio | 12.3:1 |
| Fuel System | Keihin FCR-MX39 flat-slide carburettor with throttle position sensor | Replacement Options |
| Ignition | CDI magneto |
| Spark Plug | NGK CR8E |
| Spark Plug Gap | 0.7-0.8 mm (0.028-0.031 in) |
| Cooling System | Liquid cooled |
| Starting System | Kick starter with automatic decompression and hot-start system |
Transmission
| Transmission | 4-speed constant-mesh |
| Clutch | Wet multi-plate |
| Final Drive | Chain, 14-tooth front / 48-tooth rear sprocket |
Dimensions
| Overall Length | 2,192 mm |
| Overall Width | 827 mm |
| Overall Height | 1,307 mm |
| Wheelbase | 1,485 mm |
| Ground Clearance | 381 mm |
| Seat Height | 998 mm |
| Fuel Capacity | 8.0 L |
Chassis
Suspension
| Front Suspension | 48 mm KYB inverted telescopic cartridge fork, adjustable compression and rebound damping | Fork Oil Levels |
| Front Suspension Travel | 300 mm (11.8 in) |
| Rear Suspension | Link-type Monocross with KYB gas/oil shock, adjustable spring preload, compression and rebound damping |
| Rear Suspension Travel | 315 mm (12.4 in) rear wheel travel |
| Fork Oil | Yamaha Suspension Oil 01; 48 mm KYB cartridge fork. Standard oil level approximately 125 mm from the top with fork compressed and spring removed; use model-specific service procedure when filling and bleeding. |
Brakes & Wheels
| Front Brake | Hydraulic single disc, 250 mm |
| Rear Brake | Hydraulic single disc, 245 mm |
| Front Wheel Size | 21 x 1.60 in aluminium spoked wheel |
| Rear Wheel Size | 19 x 2.15 in aluminium spoked wheel |
Service Data
| Fuel Type | Premium unleaded petrol, minimum 95 RON |
| Premix Information | Not applicable - 4-stroke engine |
| Gearbox Oil | Engine and transmission share the same dry-sump engine oil supply; approximately 1.0 L periodic oil change, 1.1 L with oil filter replacement and 1.2 L total capacity. Use API SG or higher non-friction-modified 4-stroke motorcycle oil. |
| Air Filter | Wet-type foam element |
| Service Notes | Dry-sump lubrication. Maintain frequent oil and filter changes, inspect valve clearance regularly, keep the foam air filter clean and correctly oiled, and maintain correct FCR-MX39 jetting, accelerator-pump and hot-start operation. The 2004 model retained the four-speed gearbox and steel frame of the first-generation YZ450F while receiving significant suspension and chassis refinements. |
2004 Yamaha YZ450F: Refining Yamaha's First-Generation 450
The 2004 Yamaha YZ450F was an evolutionary update to the first-generation YZ450F introduced a year earlier. Yamaha retained the basic 449 cc five-valve engine, steel semi-double-cradle frame and unusual four-speed transmission, but made a series of changes aimed at improving suspension performance, handling and overall rideability.
The engine continued with a 95.0 x 63.4 mm bore and stroke, 12.3:1 compression ratio and Keihin FCR-MX39 flat-slide carburettor. The FCR gave the YZ450F its sharp throttle response, but correct jetting, accelerator-pump operation and hot-start function remain important on surviving bikes. Owners maintaining the original carburettor can compare alternatives through the MXOwners carburettor reference.
One of the more important 2004 changes was the adoption of a 48 mm KYB inverted fork, replacing the smaller fork used on the original 2003 machine. Front travel remained around 300 mm, while the linkage-operated Monocross rear suspension continued to provide roughly 315 mm of wheel movement. Owners rebuilding the front end can consult the MXOwners fork oil reference when checking setup and servicing information.
The four-speed transmission remained one of the YZ450F's defining characteristics. Yamaha designed the ratios specifically for motocross, relying on the broad torque of the 449 cc engine to reduce the need for constant shifting. That made the bike distinctive but also means transmission parts and gearing should be checked carefully when restoring one.
For today's owner, the 2004 YZ450F represents a refined version of Yamaha's original big-bore four-stroke concept before the later move to aluminium frames and five-speed gearboxes. Model-specific components can be checked through the MXOwners Parts Finder, while the standard 80/100-21 front and 110/90-19 rear tyre sizes can be compared using the MXOwners Tyre Size Guide.
