Target Audience:
Enthusiast riders, professional mechanics, DIY mechanics working on the Yamaha YZ125.
Purpose:
To provide comprehensive repair and maintenance information for the Yamaha YZ125, enabling owners to perform a wide range of tasks.
Competitor Manuals:
This manual offers a level of detail comparable to official Yamaha factory service manuals.
Comprehensiveness:
Covers all major mechanical and electrical systems in detail.
Clarity:
Detailed instructions, clear diagrams, and easy-to-understand language.
Accessibility:
Instant digital download allows immediate access to critical repair information.
Engine Mechanical:
Complete overhaul, disassembly, assembly, inspection, and torque specifications for all internal engine components.
Fuel System:
Carburetor tuning, cleaning, overhaul, fuel pump (if applicable), fuel lines, and fuel tank service.
Ignition System:
CDI unit, spark plug inspection and replacement, stator and rotor testing, wiring diagrams.
Cooling System:
Radiator service, water pump inspection and repair, coolant type and capacity.
Transmission Drivetrain:
Clutch service, gearbox disassembly and assembly, gear inspection, shift mechanism repair, chain and sprocket maintenance.
Suspension Front:
Fork seal replacement, oil level and type, damping adjustments, spring replacement, fork leg disassembly and assembly.
Suspension Rear:
Shock absorber service, linkage bearing inspection and lubrication, spring preload adjustment, swingarm service.
Brakes Front:
Caliper overhaul, brake pad replacement, rotor inspection, brake fluid type and bleeding procedure.
Brakes Rear:
Caliper overhaul, brake pad replacement, rotor inspection, brake fluid type and bleeding procedure.
Electrical System:
Wiring diagrams, battery maintenance, lighting system, kill switch, handlebar controls, fuse box.
Chassis Frame:
Frame inspection, headstock bearing service, subframe inspection.
Bodywork Plastics:
Fairing removal and installation, seat, fuel tank cover, fender replacement.
Routine Maintenance:
Pre-ride checks, oil changes, filter cleaning/replacement, chain lubrication and adjustment.
Troubleshooting:
Diagnostic guides for common problems and symptoms, root cause analysis.
Engine Rebuild:
Complete step-by-step instructions for engine disassembly, cleaning, inspection, parts replacement, and reassembly.
Suspension Rebuild:
Detailed guides for overhauling front forks and rear shock absorbers, including seal replacement and fluid changes.
Brake Service:
Pad and rotor replacement, caliper servicing, bleeding procedures.
Electrical Diagnostics:
Using wiring diagrams to diagnose electrical faults, testing components.
Carburetor Tuning And Rebuild:
Jetting adjustments, float bowl cleaning, gasket replacement.
Diagnostic Procedures:
In-depth troubleshooting guides with symptom-based fault finding.
Repair Procedures:
Comprehensive, step-by-step instructions for all mechanical and electrical repairs.
Rebuild Instructions:
Detailed procedures for complete engine and component rebuilds.
Torque Specifications:
Precise torque values for all critical fasteners and bolts.
Wiring Diagrams:
High-quality, clear, and complete electrical system wiring diagrams.
Engine Type:
2-Stroke, Liquid-Cooled, Reed Valve Induction
Bore X Stroke Mm:
54.0 x 54.5 mm
Compression Ratio:
9.2:1 (or as specified for model year)
Carburetor Model:
Keihin PWK38S
Ignition System:
CDI Digital
Horsepower Hp:
Approx. 39-40 HP (at crankshaft, model dependent)
Torque Lb-Ft:
Approx. 17-18 lb-ft (at crankshaft, model dependent)
Fuel Type:
Unleaded gasoline (91 octane or higher recommended)
Fuel Oil Mixture:
50:1 (Yamalube 2-stroke oil or equivalent)
Fuel Tank Capacity L:
7.2 L (1.9 US gal)
Engine Oil Change:
Every 10-15 hours of riding or as specified in the manual.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Spark Plug Inspection:
Every 20-30 hours of riding.
Chain Lubrication Adjustment:
Before every ride or as needed.
Fork Oil Change:
Every 20-40 hours of riding, or as per manual recommendations for optimal performance.
Engine Oil Type:
Yamalube 2-stroke oil or equivalent (premix ratio 50:1)
Transmission Oil Type:
Yamalube SAE 10W-30 API SG or higher
Coolant Type:
Permanent type antifreeze (ethylene glycol based), 50/50 mix with distilled water.
Brake Fluid Type:
DOT 3 or DOT 4 Hydraulic Brake Fluid
Clutch Wear:
Clutch plates can wear over time, especially with aggressive riding. Manual provides replacement instructions and specifications.
Carburetor Jetting:
May require adjustment based on altitude, temperature, and modifications. Manual details the jetting process.
Suspension Seals:
Fork and shock seals can degrade and leak, requiring replacement. Manual offers detailed seal replacement procedures.
Power Valve Cleaning:
The power valve system can accumulate carbon, affecting performance. Regular cleaning is recommended as detailed in the manual.
Yamaha Legacy:
Yamaha has a long and storied history in motocross and off-road racing, with the YZ line being a cornerstone of their performance offerings.
Yz125 Development:
The YZ125 has been continuously developed and refined since its inception, focusing on lightweight design, powerful engines, and advanced suspension for competitive motocross performance.
2005 2006 Updates:
These model years represent a period of refinement for the YZ125, building on established platforms with minor tweaks to suspension, engine tuning, and aesthetics.
Manufacturing Origin:
Japan