🏷️ Basic Information

Make:

Yamaha

Model:

YZ 125

Year:

2001

Chassis Code:

4SS

Engine Code:

4SS1

Model Designator:

YZ125(N)/LC

👋 Introduction

Positioning:

The Yamaha YZ125 for 2001 was a highly competitive motocross machine, renowned for its potent two-stroke engine and agile handling. It was a staple in the 125cc class for amateur and professional racers.

Competitors:

Key competitors included the Honda CR125R, Kawasaki KX125, and Suzuki RM125 of the same era.

Features:

Powerful liquid-cooled 125cc two-stroke engine, YPVS (Yamaha Power Valve System), advanced KYB suspension, lightweight chassis, disc brakes front and rear.

📋 Manual Details

Primary Coverage:

Complete Service, Repair, and Workshop Procedures

Secondary Coverage:

Maintenance, Troubleshooting, Diagnostics, Specifications

Estimated Page Count:

~200-300 pages (typical for this era/model)

Type:

Service Manual / Workshop Manual

Language:

English

Format:

Digital Download (PDF)

📖 Manual Coverage

Engine:

Top-end, bottom-end, lubrication, cooling, ignition, carburetor, exhaust

Transmission:

Clutch, gearbox, shifting mechanism, lubrication

Chassis:

Frame, subframe, swingarm, linkages, bearings

Suspension:

Front forks (KYB Speed Sensitive System - SSS), rear shock absorber (Monocross system), adjustments, rebuilds

Brakes:

Front and rear hydraulic disc brakes, master cylinders, calipers, fluid replacement

Electrical:

Ignition system, lighting, wiring diagrams, battery, charging system (if applicable to this model's basic setup)

Wheels Tires:

Spoke tension, hub maintenance, tire selection and mounting

Controls:

Handlebars, levers, cables, footpegs, shifting and brake pedals

Maintenance:

Regular inspection, lubrication, filter changes, fluid checks and changes, spark plug replacement, chain adjustment

Repair:

Engine rebuilds (top and bottom end), transmission overhaul, carburetor tuning and rebuilding, suspension servicing, brake system repair

Troubleshooting:

Diagnostic flowcharts for common performance issues, starting problems, electrical faults

Disassembly Assembly:

Detailed step-by-step instructions for component removal and reinstallation

Adjustments:

Carburetor jetting, ignition timing, clutch engagement, suspension settings, chain slack

Troubleshooting Diagnostics:

Includes detailed troubleshooting charts and diagnostic procedures for identifying and resolving mechanical and electrical issues.

Depth:

Comprehensive, covering all aspects from basic rider maintenance to full engine and chassis overhauls

Detail Level:

Detailed specifications, torque values, clearances, and diagnostic procedures

📊 Manual Specifications

Format Type:

PDF

Searchability:

Likely searchable text if scanned professionally

Quality:

Digital, quality depends on original scan/creation

Binding:

N/A (Digital Download)

Paper:

N/A (Digital Download)

Illustration Type:

Diagrams, exploded views, line drawings

Manual Completeness:

Full factory service manual covering all aspects of repair and maintenance.

⚙️ Engine Specifications

Engine Type:

Liquid-cooled, 2-stroke, reed valve, single-cylinder

Displacement:

124cc

Bore X Stroke:

54.0 mm x 54.5 mm

Compression Ratio:

8.8:1 (at zero deck height)

Ignition:

CDI (Capacitor Discharge Ignition)

Cooling System:

Liquid Cooling (Ethylene Glycol & Water Mixture)

Reed Valve Type:

Petal reed valve

Horsepower:

Approx. 35-40 HP (at crankshaft, estimated)

Torque:

Not officially published for this model year, but significant for class

Peak Rpm:

Not officially specified, but typically in the 11,000-12,000 RPM range for this engine.

Carburetor:

Keihin PWK38S (38mm flat-slide)

Fuel Type:

Unleaded gasoline with 2-stroke oil mixture (50:1 ratio recommended)

Fuel Tank Capacity:

8.0 Liters (2.1 US gal)

🔧 Transmission

Transmission Type:

Constant-mesh 6-speed sequential

Clutch:

Wet, multi-plate

Final Drive:

O-ring sealed chain

Transmission Oil Type:

Yamalube 4 (or equivalent SAE 10W-30 API SE Type SF, SG, SH, SJ or higher)

Transmission Oil Capacity:

1.0 Liters (1.05 US qt)

Gear Ratios:

Gear ratios are specific and detailed within the manual, crucial for performance tuning.

📐 Dimensions

Length:

2155 mm (84.8 in)

Width:

830 mm (32.7 in)

Height:

1270 mm (50.0 in)

Seat Height:

975 mm (38.4 in)

Wheelbase:

1455 mm (57.3 in)

Ground Clearance:

340 mm (13.4 in)

Dry Weight:

94 kg (207.2 lbs)

Wet Weight:

Approx. 103 kg (227 lbs) (with all fluids, estimated)

Front Tire:

80/100-21 51M

Rear Tire:

110/90-19 62M

Wheelbase Spokes:

Front: 36, Rear: 36

Front Fork Travel:

295 mm (11.6 in)

Rear Shock Travel:

310 mm (12.2 in)

🛡️ Safety Features

Safety Standards:

N/A (Motocross specific vehicle, not road legal)

Braking System:

Hydraulic disc brakes front and rear for superior stopping power

Frame Construction:

Strong steel frame designed for high-impact off-road use

💡 Technology Features

Infotainment Features:

N/A (Pure Motocross Vehicle - no infotainment systems)

Assistance Features:

N/A (Pure Motocross Vehicle - no electronic driver assistance)

Connectivity Features:

N/A (Pure Motocross Vehicle - no connectivity)

🔧 Maintenance

Oil Change Transmission:

Every 20-30 hours of riding, or annually.

Air Filter Cleaning:

Clean after every few rides or as needed, especially in dusty conditions.

Spark Plug Replacement:

Inspect every 10-15 hours, replace as needed. Recommended plug: NGK BR8ES.

Chain Lubrication Adjustment:

Lubricate every 5-10 hours, adjust slack every 10-15 hours.

Top End Rebuild:

Recommended every 40-60 hours of hard use.

Suspension Service:

Fork oil change recommended every 20-30 hours; rear shock service as needed or per manual intervals.

Coolant:

Yamaha Coolant (or equivalent) - 50:50 mix of ethylene glycol and distilled water.

Brake Fluid:

DOT 4 hydraulic brake fluid.

2 Stroke Oil:

Yamalube 2R (or equivalent high-performance 2-stroke racing oil) mixed at 50:1 ratio with fuel.

Carburetor Jetting:

Can be sensitive to altitude and temperature changes; requires periodic jetting adjustments for optimal performance.

Clutch Wear:

Clutch plates and springs can wear out with aggressive riding and should be inspected regularly.

Suspension Seals:

Fork seals and rear shock seals can degrade over time, leading to oil leaks and requiring replacement.

Ypvs System:

The power valve mechanism can accumulate carbon deposits, requiring cleaning and servicing to maintain proper operation.

📚 Vehicle History

Brand History:

Yamaha has a long and storied history in motorcycle racing, particularly in motocross, dating back to the early days of the sport. The YZ line has consistently been at the forefront of motocross technology.

Yz125 Evolution:

The YZ125 has undergone continuous evolution since its inception. The 2001 model represented a significant step in performance and suspension technology compared to earlier generations, featuring improvements in engine power delivery and chassis dynamics.

Production Era:

The YZ125 has been in continuous production for decades, with the 2001 model being part of the highly successful third generation (1996-2001) which saw substantial performance gains.

🏆 Awards & Recognition

Motocross Awards:

While specific awards for the 2001 YZ125 might not be widely documented, Yamaha's YZ line consistently received praise and accolades from motocross publications for its performance and innovation throughout the late 1990s and early 2000s.