2018 Yamaha YZ250
General Specifications
| Model | Yamaha YZ250 |
| Year | 2018 |
| Category | Motocross / Competition Off-Road |
| Engine Type | Liquid-cooled, single-cylinder, 2-stroke, reed-valve induction with Yamaha Power Valve System (YPVS) |
| Weight | 103 kg (227 lb) wet / curb weight |
Engine
| Displacement | 249 cc |
| Bore x Stroke | 66.4 x 72.0 mm |
| Compression Ratio | 8.9–10.6:1 |
| Fuel System | Keihin PWK38S, 38 mm flat-slide carburettor with throttle-position sensor, power jet and reed-valve induction | Replacement Options |
| Ignition | Digital CDI magneto ignition |
| Spark Plug | NGK BR8EG (resistor type) |
| Spark Plug Gap | 0.5–0.6 mm (0.020–0.024 in) |
| Cooling System | Liquid-cooled, twin radiators |
| Starting System | Kick starter |
Transmission
| Transmission | 5-speed constant-mesh manual |
| Clutch | Wet, multi-plate, coil-spring, cable-operated |
| Final Drive | Chain drive; standard gearing 14T front / 50T rear (3.571:1) |
Dimensions
| Overall Length | 2,147 mm (84.5 in) |
| Overall Width | 827 mm (32.6 in) |
| Overall Height | 1,299 mm (51.1 in) |
| Wheelbase | 1,446 mm (56.9 in) |
| Ground Clearance | 367 mm (14.4 in) |
| Seat Height | 976 mm (38.4 in) |
| Fuel Capacity | 8.0 litres (2.1 US gal) |
Chassis
| Frame | Aluminium semi-double-cradle frame with removable aluminium rear subframe |
| Front Tyre | 80/100-21 51M, tube type | Tyre Size Guide |
| Rear Tyre | 110/90-19 62M, tube type | Tyre Size Guide |
Suspension
| Front Suspension | 48 mm KYB upside-down Speed Sensitive System (SSS) twin-chamber coil-spring cartridge forks with adjustable compression and rebound damping | Fork Oil Levels |
| Front Suspension Travel | 300 mm (11.8 in) |
| Rear Suspension | KYB gas/oil-damped Monocross linkage shock with adjustable spring preload, high-speed and low-speed compression damping and rebound damping |
| Rear Suspension Travel | 315 mm (12.4 in) |
| Fork Oil | Yamaha Suspension Oil S1. KYB twin-chamber forks: inner damper initial filling quantity 205 mL (6.93 US oz) per leg, followed by bleeding and discharge of excess oil according to the service procedure. Outer chamber standard oil quantity 320 mL (10.8 US oz) per leg; adjustment range 300–365 mL. Inner and outer chambers must be serviced separately. Total fork oil capacity listed in the service specifications: 515 mL per leg. |
Brakes & Wheels
| Front Brake | Hydraulic single disc, 250 mm rotor (2018 European specification), twin-piston caliper |
| Rear Brake | Hydraulic single disc, 245 mm rotor, single-piston caliper |
| Front Wheel Size | 21 x 1.60-inch aluminium spoked rim |
| Rear Wheel Size | 19 x 2.15-inch aluminium spoked rim |
Service Data
| Fuel Type | Premium unleaded petrol mixed with suitable competition-grade 2-stroke oil; use fuel meeting the applicable regional Yamaha octane requirement |
| Premix Information | 30:1 petrol-to-oil ratio using Yamaha Yamalube 2-R or suitable equivalent competition-grade 2-stroke oil. Approximately 33.3 mL oil per litre of petrol. Yamaha specifies a richer 15:1 mixture for initial engine break-in | Premix Calculator |
| Gearbox Oil | Yamalube SAE 10W-40 motorcycle oil, API SG or higher, JASO MA. Periodic transmission oil change: 0.75 L (750 mL). Total transmission oil capacity: 0.80 L (800 mL). |
| Air Filter | Reusable, oil-treated foam air-filter element; use Yamaha foam air-filter oil or equivalent |
| Service Notes | The 2018 YZ250 was substantially carried over from the 2017 model, retaining the established engine, aluminium chassis and KYB SSS suspension. Maintain the specified 30:1 fuel premix for normal operation and follow Yamaha's separate break-in instructions when applicable. Carburettor jetting varies by region and should be adjusted for temperature, altitude and fuel. Spark plug: NGK BR8EG with 0.5–0.6 mm gap. Transmission oil should be replaced every race under Yamaha's competition maintenance schedule, approximately 2.5 operating hours. Transmission drain bolt tightening torque: 23 Nm (17 ft-lb). Inspect piston, rings, reed valves and YPVS components regularly. Clean and oil the foam air filter after dusty riding. Check fork seals, steering-head bearings, suspension linkage bearings, wheel bearings, coolant, brake pads, spoke tension and drive-chain adjustment. The YZ250 motocross model differs from the YZ250X cross-country model in transmission ratios, suspension settings and equipment. Confirm regional brake specifications and model identification before purchasing replacement components. |
2018 Yamaha YZ250 – A Two-Stroke Survivor with a Proven Racing Heritage
The 2018 Yamaha YZ250 continued one of motocross racing's most enduring two-stroke traditions. While other manufacturers concentrated heavily on four-stroke development, Yamaha maintained its familiar 249cc two-stroke motocross machine. The 2018 model was substantially unchanged from 2017, with updated graphics rather than a major mechanical redesign. Its continued production reflected the lasting appeal of a lightweight, responsive motorcycle built around straightforward competition engineering.
The YZ250's aluminium frame originated with the major 2005 redesign, while its highly regarded KYB Speed Sensitive System suspension arrived in 2006. Yamaha refreshed the bodywork and suspension specification in 2015, giving the motorcycle a more contemporary appearance without abandoning its proven mechanical foundation. By 2018, this combination had become well established among motocross riders.
The liquid-cooled engine retained Yamaha's Power Valve System, a 38 mm Keihin PWK carburettor and five-speed transmission. Its strong midrange acceleration and immediate throttle response remained defining characteristics. Correct fuel mixture and carburettor jetting were essential for consistent performance, particularly when riding at different temperatures or elevations. Owners investigating carburettor maintenance can explore the MXOwners carburettor information and replacement options.
Suspension remained another major strength. The 48 mm KYB SSS forks provided 300 mm of travel, complemented by a fully adjustable rear Monocross shock offering 315 mm. Correct spring rates, damping adjustments and regular servicing help preserve the handling qualities for which the YZ250 became known. Owners servicing the twin-chamber forks can consult the MXOwners fork oil reference guide for additional maintenance information.
For today's owners, the 2018 YZ250 offers the advantages of an established design and extensive aftermarket support. Regular piston inspections, clean air filters, fresh gearbox oil and attention to suspension bearings are important for reliability. Replacement components can be investigated through the MXOwners motorcycle parts finder. Although the 2018 model introduced few new features, it demonstrated why Yamaha's traditional two-stroke motocross motorcycle continued to attract riders long after much of the industry had shifted towards four-stroke competition machines.
