🏷️ Basic Information

Make:

Yamaha

Model:

YZ250

Year:

1991

Vehicle Type:

Motorcycle

Engine Configuration:

2-Stroke

Chassis Code:

Refer to Manual for Specific Codes (e.g., 37X)

Engine Code:

Refer to Manual for Specific Codes (e.g., 5ES)

👋 Introduction

Positioning:

The 1991 Yamaha YZ250 was a top-tier motocross machine, known for its potent 2-stroke power delivery and competitive chassis. This manual targets owners and mechanics seeking in-depth knowledge for maintaining and repairing this specific model.

Competitors:

Competed directly with other 250cc motocross bikes of the era, such as the Honda CR250R, Kawasaki KX250, and Suzuki RM250.

Bike Features:

Liquid-cooled 2-stroke engine, aggressive styling, advanced suspension for its time, strong performance characteristics favored by racers.

Value Proposition:

Essential for anyone looking to perform in-depth maintenance, diagnosis, or restoration on a 1991 Yamaha YZ250, ensuring optimal performance and longevity.

📋 Manual Details

Primary Coverage:

Comprehensive Service, Repair, and Workshop Procedures

Secondary Coverage:

Troubleshooting, Diagnostics, Maintenance Schedules, Technical Specifications

Estimated Page Count:

Approximately 300-500 pages (typical for this era and type of manual)

Type:

Service Repair Workshop Manual

Language:

English

Format:

Digital Download (PDF)

📖 Manual Coverage

Engine:

Top-end rebuild (cylinder, piston, rings), bottom-end rebuild (crankshaft, bearings), carburetor tuning and overhaul, ignition system (CDI, spark plug), cooling system (air-cooled), exhaust system.

Transmission:

Clutch operation and adjustment, gearbox overhaul, gear selection mechanisms, lubrication.

Chassis And Suspension:

Front fork service (oil change, seal replacement, spring replacement), rear shock absorber service and adjustment, swingarm and linkage maintenance, steering system overhaul.

Brakes:

Front and rear hydraulic brake system service (fluid replacement, caliper overhaul, master cylinder maintenance), brake pad replacement, rotor inspection.

Electrical:

Wiring diagrams, lighting system maintenance, ignition coil testing, battery maintenance, component testing (switches, sensors).

Fuel System:

Fuel tank maintenance, fuel line inspection, fuel filter replacement (if applicable), carburetor jetting and settings.

Bodywork And Frame:

Panel removal and installation, seat maintenance, handlebar and control adjustments, frame inspection.

Maintenance:

Regular maintenance checks, lubrication points and intervals, filter replacements, fluid level checks, general tune-up procedures.

Repair:

Complete disassembly and reassembly procedures for all major components, component-specific repair instructions, troubleshooting guides for common failures.

Troubleshooting:

Diagnostic trees for common performance issues, electrical faults, starting problems, and operational anomalies.

Technical Data:

Torque specifications for critical fasteners, engine timings, clearances, fluid capacities, and electrical specifications.

Depth:

Comprehensive, covering basic maintenance to full engine and transmission rebuilds. Includes detailed diagnostic information.

📊 Manual Specifications

Format:

PDF (Portable Document Format)

Searchability:

Likely searchable text content for quick information retrieval.

Quality:

High-resolution scans of original documentation, ensuring clear images and readable text.

Type:

N/A (Digital Download)

Type:

N/A (Digital Download)

⚙️ Engine Specifications

Type:

Liquid-cooled, 2-stroke, reed valve inducted

Displacement:

249cc (approx.)

Bore X Stroke:

Refer to Manual for Specific Dimensions (e.g., 68.0 mm x 68.6 mm)

Compression Ratio:

Refer to Manual for Specific Ratio (e.g., 7.9:1)

Horsepower:

Approx. 45-50 HP (estimated, actual figures vary)

Torque:

Refer to Manual for Specific Torque Figures

Carburetor Model:

Mikuni VM Series (e.g., VM38SS)

Fuel Type:

Unleaded gasoline with 2-stroke oil premix

Premix Ratio:

Refer to Manual for Recommended Ratio (typically 20:1 or 32:1)

Ignition System:

CDI (Capacitor Discharge Ignition)

Type:

Premix or Autolube system (refer to manual for specific configuration)

🔧 Transmission

Type:

6-speed constant mesh manual transmission

Type:

N/A (Standard configuration for this model)

Clutch Type:

Wet, multi-plate

Gear Ratios:

Refer to Manual for Specific Gear Ratios

Transmission Oil Type:

Yamalube 10W or equivalent API GL-4, SAE 80 hypoid gear oil (refer to manual for exact specification)

Transmission Oil Capacity:

Refer to Manual for Specific Capacity (e.g., 0.8 L)

📐 Dimensions

Overall Length:

Refer to Manual for Specific Dimensions

Overall Width:

Refer to Manual for Specific Dimensions

Overall Height:

Refer to Manual for Specific Dimensions

Wheelbase:

Refer to Manual for Specific Wheelbase

Dry Weight:

Approx. 98 kg (216 lbs) (typical for this model)

Wet Weight:

Refer to Manual for Specific Wet Weight

Front Tire Size:

80/100-21 46M (typical)

Rear Tire Size:

110/90-18 61M (typical)

Front Wheel:

21-inch spoke wheel

Rear Wheel:

18-inch spoke wheel

🛡️ Safety Features

Crash Test Ratings:

N/A (Motorcycles are not subject to the same crash test ratings as cars)

Braking System:

Hydraulic disc brakes front and rear

Frame Construction:

Steel semi-double cradle frame for rigidity and durability

💡 Technology Features

System:

N/A (Motorcycle)

Features:

N/A (Motorcycle)

Features:

N/A (Motorcycle)

🔧 Maintenance

Air Filter Cleaning:

After every few rides, depending on conditions (refer to manual for specifics).

Spark Plug Inspection:

Regular inspection and replacement as needed (refer to manual for recommended replacement interval).

Oil Change Transmission:

Every 10-15 hours of operation or annually (refer to manual for precise interval).

Fork Oil Change:

Recommended every 15-20 hours of operation or annually.

Piston Ring Replacement:

Typically recommended every 30-50 hours of hard riding for optimal performance, or as indicated by compression loss.

Coolant Type:

Ethylene glycol-based coolant with a 50/50 mix of distilled water (refer to manual for exact specification).

Brake Fluid Type:

DOT 3 or DOT 4 hydraulic brake fluid (refer to manual for precise specification).

2 Stroke Oil Type:

High-quality 2-stroke racing oil designed for premix or injection systems (refer to manual).

Common Problems:

Worn crankcase seals leading to air leaks, carburetor jetting sensitivity to altitude and temperature, clutch wear, suspension seal leaks, exhaust power valve sticking (if equipped).

Preventative Maintenance:

Regularly clean the air filter, check for air leaks, maintain correct fuel/oil mix, adjust carburetor for conditions, and perform timely transmission oil changes.

📚 Vehicle History

Heritage:

Yamaha has a long and successful history in motorcycle racing, particularly in motocross, with the YZ series being a cornerstone of their off-road performance lineup.

Evolution:

The YZ250 has undergone continuous evolution since its inception, with each generation introducing advancements in engine technology, suspension, and chassis design. The 1991 model represented a significant iteration in this development cycle.

Production Period:

The YZ250 has been in continuous production for decades, with the 1991 model belonging to a generation that saw strong competition and refinement.

Racing Impact:

YZ models have a storied racing history, contributing to numerous championships and setting performance benchmarks in their respective classes.

🏆 Awards & Recognition

Awards:

While specific awards for the 1991 YZ250 are not readily documented, the YZ series has historically been recognized in motorsport publications and by riders for its performance and competitive edge.