🏷️ Basic Information

Make:

Yamaha

Model:

YZ125

Year:

2005

Engine Code Designation:

125cc Two-Stroke

Vin Decoder Key:

Refer to manual for specific VIN structure

👋 Introduction

Motorcycle Segment:

Motocross/Off-Road Competition

Target Audience:

Motocross racers, off-road enthusiasts, and DIY mechanics performing maintenance and repairs on the YZ125.

Key Competitors 2005:

Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125 SX.

Yz125 Reputation:

Renowned for its potent two-stroke engine, agile handling, and competitive performance in the 125cc class.

Manual Value Proposition:

Essential resource for maintaining the performance, reliability, and longevity of the 2005 Yamaha YZ125.

📋 Manual Details

Primary Coverage:

Yamaha YZ125 2005 Model Year

Secondary Coverage:

Similar years and models (as indicated in product description, user to verify compatibility)

Estimated Page Count:

500+

Manual Type:

Service Repair Workshop Manual

Language:

English

Format:

Digital (likely PDF, based on typical online sales)

📖 Manual Coverage

Engine:

Complete disassembly, inspection, repair, and assembly of the 125cc two-stroke engine, including top-end (cylinder, piston, rings), bottom-end (crankshaft, connecting rod, bearings), and cooling system (if applicable).

Fuel System:

Carburetor tuning, jetting, and overhaul; fuel lines, fuel tank inspection and cleaning.

Ignition System:

CDI unit, spark plug specifications, ignition timing, stator and coil testing.

Transmission:

Gearbox disassembly, inspection, and repair; clutch operation and service; shift mechanism.

Suspension:

Front fork (USD) overhaul, oil change, seal replacement, and adjustment; rear shock absorber service, linkage maintenance, and adjustment.

Brakes:

Front and rear hydraulic disc brake system service, caliper overhaul, master cylinder service, pad replacement, fluid flush and bleeding (DOT 4 recommended).

Electrical System:

Wiring diagrams, lighting circuits, battery maintenance, troubleshooting of electrical faults.

Chassis Frame:

Frame inspection, steering head bearing service, general chassis component checks.

Bodywork Fairings:

Fairing removal and installation, seat, fuel tank, and fender maintenance.

Cooling System:

Radiator inspection, coolant flush and replacement (if applicable to this specific YZ125 generation - often air-cooled for this era, but manual will clarify).

Preventative Maintenance:

Regularly scheduled inspections, lubrication points, filter replacement (air, oil if applicable), chain adjustment and lubrication.

Troubleshooting:

Systematic diagnostic procedures for common and uncommon problems, including no-start conditions, poor performance, and electrical faults.

Engine Rebuilding:

Detailed instructions for complete engine overhauls, including piston ring gap, cylinder bore honing, crankshaft runout, and bearing clearances.

Suspension Servicing:

Step-by-step guides for fork seal replacement, oil level and type specifications, and rear shock absorber maintenance.

Brake System Maintenance:

Complete guide to brake fluid replacement, caliper piston retraction, and bleeding procedures.

Carburetor Overhaul:

Detailed instructions for cleaning, re-jetting, and adjusting the carburetor for optimal performance and altitude compensation.

Electrical Diagnostics:

Guidance on using multimeters to test components like the stator, CDI, and ignition coils, along with interpreting wiring diagrams.

Wheel And Tire Service:

Tire changing, tube replacement, spoke tensioning (if applicable), and wheel balancing.

Clutch Adjustment And Service:

Proper adjustment of clutch cable and lever free play, clutch plate replacement procedures.

Depth Of Coverage:

Comprehensive - covers everything from basic owner maintenance to complete engine and chassis rebuilds, including detailed specifications and troubleshooting guides.

📊 Manual Specifications

Digital File Type:

PDF (Portable Document Format)

Searchability:

Likely text-searchable if professionally scanned, allowing for quick access to information.

Print Readability:

High clarity, designed for clear reproduction of diagrams and text.

Binding Type:

N/A (Digital Format)

Paper Type:

N/A (Digital Format)

⚙️ Engine Specifications

Engine Type:

124cc Liquid-Cooled, Reed-Valve, Two-Stroke

Bore X Stroke:

54.0 mm x 54.5 mm

Compression Ratio:

8.2:1

Power Valve System:

Yamaha Power Valve System (YPVS) for improved powerband and torque.

Horsepower:

Approx. 38-40 HP (at crankshaft, model specific tuning may vary)

Torque:

Approx. 18-19 lb-ft (at crankshaft, model specific tuning may vary)

Carburetor Type:

Keihin PWK38S (38mm Slide Valve, Dual Diffuser)

Fuel Type Recommendation:

Unleaded gasoline with a minimum octane rating of 91 (AKI).

Oil Fuel Mixture:

Typically 50:1 ratio with high-quality 2-stroke premix oil.

Coolant Type:

Yamaha-specific coolant or equivalent permanent type antifreeze (50% solution).

Transmission Oil Type:

Yamalube Gear Oil (SAE 10W-30 API GL-4) or equivalent.

🔧 Transmission

Transmission Type:

Constant Mesh, 6-speed

Clutch Type:

Wet, Multi-Plate

Clutch Operation:

Hydraulically Actuated

1St Gear:

2.333 (35/15)

2Nd Gear:

1.750 (28/16)

3Rd Gear:

1.400 (28/20)

4Th Gear:

1.182 (26/22)

5Th Gear:

1.045 (23/22)

6Th Gear:

0.958 (23/24)

📐 Dimensions

Overall Length:

2,155 mm (84.8 in)

Overall Width:

825 mm (32.5 in)

Overall Height:

1,270 mm (50.0 in)

Seat Height:

970 mm (38.2 in)

Wheelbase:

1,475 mm (58.1 in)

Dry Weight:

92 kg (202.6 lbs)

Fuel Tank Capacity:

8.0 L (2.1 US gal)

🛡️ Safety Features

Safety Standards:

N/A (Off-road competition vehicle, not typically rated by NHTSA or Euro NCAP)

Braking System:

Hydraulic dual-piston front caliper with 250mm disc; Hydraulic single-piston rear caliper with 245mm disc.

Chassis Design:

Rigid steel frame and aluminum subframe designed for motocross agility and durability.

💡 Technology Features

Infotainment System:

N/A (Pure motocross competition machine, no infotainment features).

Driver Assistance Features:

N/A (No electronic rider aids).

Connectivity Features:

N/A (No electronic connectivity features).

🔧 Maintenance

Air Filter Cleaning:

Every 10-15 hours of riding, or more frequently in dusty conditions.

Spark Plug Replacement:

Every 20-30 hours of riding, or as needed based on inspection.

Chain Lubrication Adjustment:

Every 5-10 hours of riding, or after washing/wet conditions.

Transmission Oil Change:

Every 20-30 hours of riding, or annually.

Top End Rebuild Recommendation:

Typically 50-100 hours for piston and rings, depending on riding style and maintenance. Crankshaft and bearings may last significantly longer.

Fork Oil Type:

Yamalube Fork Oil 01 (Equivalent to SAE 5W) or specified alternative in the manual.

Fork Oil Level:

Refer to manual for precise oil level (e.g., 115 mm from top of inner tube with spring removed).

Common Wear Items:

Piston rings, clutch plates, wheel bearings, steering head bearings, swingarm pivot bearings, fork seals, brake pads.

Performance Tuning Considerations:

Carburetor jetting for altitude and temperature, exhaust pipe condition, and reed valve condition are critical for optimal power delivery.

Ypvs Maintenance:

The YPVS power valve mechanism requires periodic cleaning to prevent carbon buildup and ensure smooth operation. Failure to do so can affect power delivery.

📚 Vehicle History

Yamaha Motorsports Legacy:

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

Yz125 Development:

The YZ125 has undergone continuous evolution since its introduction, with Yamaha consistently refining engine performance, suspension, and chassis dynamics to remain competitive.

2005 Model Updates:

Specific updates for 2005 included refinements to the YPVS system, revised suspension settings, and potentially minor chassis or bodywork tweaks to optimize performance.

Manufacturing Location:

Japan (Typically)

🏆 Awards & Recognition

Motocross Championships:

The YZ125 platform has been instrumental in numerous amateur and professional motocross championships worldwide, validating its performance capabilities.

Industry Reviews 2005:

Generally received positive reviews for its strong engine, nimble handling, and competitive pricing within the 125cc motocross class for the 2005 model year.