🏷️ Basic Information

Make:

Yamaha

Model:

YZ250

Year:

1986

Model Code:

YZ250U

👋 Introduction

Segment:

Motocross Competition Motorcycle

Reputation:

Renowned for its potent two-stroke engine and competitive performance in its era.

Rivals:

Honda CR250R, Kawasaki KX250, Suzuki RM250

Engine Technology:

Liquid-cooled, reed valve induction, Yamaha Power Valve System (YPVS)

Suspension Technology:

KYB Speed-Sensitive System (SSS) front forks, Monocross rear suspension system.

📋 Manual Details

Primary Focus:

Service, Repair, Workshop

Estimated Pages:

300+

Type:

Factory Service Manual

Language:

English

Format:

Digital (PDF)

📖 Manual Coverage

Engine:

Complete overhaul, tuning, carburetor, cooling system, lubrication, ignition system, power valve operation.

Transmission:

Clutch, gearbox, shift mechanism, lubrication, internal components.

Chassis Suspension:

Front forks (KYB Speed-Sensitive System), rear monoshock (Monocross), bearings, linkages, adjustments.

Brakes:

Front disc brake system (hydraulic), rear drum brake system, fluid types, bleeding procedures, pad replacement.

Electrical:

Ignition system, lighting, wiring diagrams, component testing, troubleshooting.

Bodywork:

Plastics, seat, fuel tank, handlebars, controls, disassembly and reassembly.

Maintenance:

Regular servicing, lubrication points, filter changes, spark plug maintenance, chain adjustment.

Troubleshooting:

Step-by-step diagnostic procedures for common and complex issues, fault finding charts.

Repair:

Detailed instructions for component replacement, disassembly, assembly, and adjustments.

Overhaul:

Complete engine and transmission rebuild procedures with torque specifications and clearances.

Depth:

Comprehensive, from basic rider maintenance to full workshop rebuilds and diagnostics.

📊 Manual Specifications

Digital Format:

PDF

Clarity:

High-resolution scans for clear text and diagrams.

Binding Format:

N/A (Digital)

Paper Quality:

N/A (Digital)

⚙️ Engine Specifications

Type:

2-Stroke, Single Cylinder

Displacement:

249 cc (250cc class)

Bore X Stroke:

68.0 mm x 68.5 mm

Cooling:

Liquid-cooled

Induction:

Reed valve

Power Valve:

Yamaha Power Valve System (YPVS)

Horsepower:

Approx. 48-50 HP (estimated, subject to tuning and specific dyno results)

Torque:

Approx. 30-32 lb-ft (estimated)

Carburetor:

Mikuni VM34SS (likely)

Fuel Type:

Unleaded gasoline with 2-stroke oil mix (e.g., 40:1)

System:

Premix

🔧 Transmission

Type:

6-speed constant mesh

Type:

Wet, multiple-disc

Drive Type:

Chain drive

📐 Dimensions

Length:

Approx. 84.6 inches (2150 mm)

Width:

Approx. 32.1 inches (815 mm)

Height:

Approx. 50.8 inches (1290 mm)

Wheelbase:

Approx. 57.7 inches (1465 mm)

Ground Clearance:

Approx. 13.2 inches (335 mm)

Dry Weight:

Approx. 225 lbs (102 kg)

Fuel Tank Capacity:

2.6 gallons (9.8 Liters)

Oil Capacity:

N/A (Premix)

Transmission Oil Capacity:

Approx. 0.75 Liters (Yamalube SAE 80 or equivalent)

🛡️ Safety Features

Safety Certification:

N/A (Competition Motorcycle)

Brakes:

Hydraulic front disc, drum rear brake

Frame:

Steel semi-double cradle frame for rigidity and handling

💡 Technology Features

Infotainment System:

N/A (Competition Motorcycle)

Rider Aids:

N/A (Focus on rider control and mechanical feedback)

🔧 Maintenance

Air Filter Cleaning:

After every few rides, or as conditions dictate (depending on dust/mud).

Spark Plug Replacement:

Every 20-40 hours of operation, or as needed based on inspection.

Chain Lubrication Adjustment:

Regularly (e.g., every 100-200 miles or as needed).

Engine Top End Rebuild:

Varies greatly with usage and maintenance, typically 50-100 hours for piston and rings.

Transmission Oil:

Yamalube Gear Oil SAE 80W, or equivalent API GL-4 specification.

Coolant:

Permanent type antifreeze (ethylene glycol based) mixed with distilled water (50/50 ratio).

Brake Fluid:

DOT 3 or DOT 4 hydraulic brake fluid.

Premix Oil:

High-quality 2-stroke motorcycle oil, specifically formulated for racing and premix applications. Refer to manual for specific JASO FD or API TC recommendations.

Clutch Wear:

Clutch plates can wear over time, especially under aggressive riding conditions. Regular adjustment and inspection are key.

Ypvs Maintenance:

The YPVS system (power valve) requires periodic cleaning and lubrication to ensure proper operation and prevent sticking.

Carburetor Tuning:

As with any 2-stroke, proper jetting and carburetor tuning are crucial for optimal performance and engine longevity. Changes in altitude or temperature can necessitate adjustments.

📚 Vehicle History

Yamaha Offroad Legacy:

Yamaha has a long and storied history in off-road and motocross racing, dating back to the early 1970s.

Yz Series Development:

The YZ series has continuously evolved, introducing innovations like the Monocross suspension and YPVS system that set industry standards.

1986 Model Year:

The 1986 YZ250 represented a significant update, incorporating advanced suspension and engine technologies for improved performance.

Previous Models:

The YZ250 lineage began in the mid-1970s and saw many iterative improvements in engine design, suspension, and chassis.

🏆 Awards & Recognition

Motocross Accolades:

While specific awards for the 1986 model aren't typically cataloged like consumer cars, the YZ250 series has consistently been a top contender in motocross racing circuits globally throughout its production run.

Editorial Reviews:

Contemporary reviews often praised the YZ250's potent engine, advanced suspension for its time, and competitive chassis balance.