Category:
Competition Motocross Bike
Era:
Early 2000s motocross technology.
Competitors:
Honda CR250R/CRF450R, Suzuki RM250/RM-Z450, Kawasaki KX250/KX450F, KTM EXC/SX.
Engine Type:
Liquid-cooled, DOHC, 4-valve, 4-stroke Single.
Suspension Type:
Upside-down telescopic front forks, Monocross rear suspension.
Performance Focus:
High-revving engine, agile handling, competitive power delivery for motocross racing.
Engine Overhaul:
Complete disassembly, inspection, repair, and reassembly of the 4-stroke engine.
Fuel System:
Carburetor tuning, cleaning, and overhaul; fuel pump diagnosis (if applicable).
Ignition System:
CDI unit, spark plug inspection and replacement, ignition timing.
Transmission:
Gearbox inspection, repair, clutch service, and lubrication.
Suspension:
Front fork (USD) and rear shock absorber service, adjustments, and seal replacement.
Brakes:
Front and rear brake caliper service, hydraulic system bleeding, pad replacement, rotor inspection.
Electrical System:
Wiring diagrams, lighting, battery maintenance, starter system troubleshooting.
Cooling System:
Radiator, hoses, and coolant specifications (though YZ426F is liquid-cooled, this is standard for comprehensive manuals).
Frame And Bodywork:
Chassis inspection, plastic component removal and installation, seat and fuel tank servicing.
Wheels And Tires:
Tire pressure, wheel bearing service, spoke tensioning.
Routine Maintenance:
Oil changes, filter replacements, chain adjustment, lubrication points.
Troubleshooting Guides:
Diagnostic flowcharts for common performance issues and system failures.
Rebuild Procedures:
Step-by-step guides for major component overhauls (engine, transmission, suspension).
Adjustment Procedures:
Carburetor idle and mixture, clutch free play, suspension settings.
Torque Specifications:
Detailed torque values for critical fasteners across all systems.
Diagnostic Checks:
Procedures for checking compression, ignition timing, and electrical continuity.
Depth:
In-depth technical information suitable for professional mechanics and experienced DIY enthusiasts.
Engine Type:
4-stroke, Liquid-cooled, DOHC, 4-valve, Single Cylinder
Bore X Stroke:
95.0 mm x 60.8 mm
Compression Ratio:
12.3:1
Lubrication System:
Wet Sump (internal oil reservoir)
Horsepower Estimate:
Approx. 45-50 HP (at crankshaft)
Torque Estimate:
Approx. 30-35 lb-ft (at crankshaft)
Carburetor:
Keihin FCR 39mm Flat Slide
Fuel Type:
Unleaded Gasoline (91 octane or higher recommended)
Fuel Capacity:
2.3 Gallons (8.7 Liters)
Safety Ratings:
Not applicable for off-road competition motorcycles.
Brakes:
Hydraulic disc brakes (front and rear)
Tires:
Knobby off-road tires for maximum traction.
Frame Construction:
Aluminum alloy frame (e.g., YZ's signature 'Deltabox' style)
Handlebars:
Fat-bar style handlebars for improved durability and rider control.
Engine Oil Change:
Every 10-15 hours of riding or as specified in manual (e.g., 1500-2000 km).
Oil Filter Replacement:
At every oil change.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Spark Plug Inspection:
Every 20-30 hours of riding.
Valve Clearance Check:
Every 20-30 hours of riding.
Engine Oil:
Yamalube 4 (or equivalent) SAE 10W-40, API SG or higher, JASO MA compliant.
Coolant:
High-quality ethylene glycol based coolant with distilled water (50:50 mix), pre-diluted coolant also acceptable.
Brake Fluid:
DOT 4 hydraulic brake fluid.
Fork Oil:
Yamaha Fork Oil G10 (or equivalent) SAE 10W. Check manual for specific volume and level.
Carburetor Jetting:
Can require meticulous jetting for optimal performance across different altitudes and conditions.
Valve Adjustment Frequency:
Valves can be prone to tightening; regular checks are crucial.
Decompressor Mechanism:
Can sometimes seize or require adjustment, affecting starting.
Oil Consumption:
Like many high-performance 4-strokes of this era, may consume some oil under hard use.
Manufacturer:
Yamaha Motor Company, renowned for its performance motorcycles, particularly in off-road disciplines.
Yz Series:
The YZ426F replaced the YZ400F and was a significant step forward in 4-stroke motocross technology, paving the way for the YZ450F.
Four Stroke Advancement:
Yamaha was a pioneer in bringing competitive 4-stroke motocross bikes to market, challenging the dominance of 2-strokes.
Production Years:
The YZ426F was produced from 1998 (as YZ400F) through 2002, with 2001 being a key year in its development.
Motocross Popularity:
Highly regarded in its class for its powerful engine and competitive chassis, popular among racers and enthusiasts.
Review Sentiment:
Generally positive reviews for power and handling, but often noted for maintenance requirements compared to 2-strokes.
Emissions Certification:
Not applicable for off-road competition motorcycles.
