Vehicle Segment:
Lightweight Dual-Sport / Enduro Motorcycle
Key Competitors Era:
Honda CR125R, Kawasaki KX125, Suzuki RM125 (motocross variants); various enduro machines.
Dt125R Reputation:
Known for its reliability, off-road capability, and relatively simple yet effective two-stroke engine.
Value Proposition:
Essential resource for owners and mechanics to maintain and repair the DT125/DT125R, ensuring longevity and optimal performance.
Engine System:
Complete overhaul, diagnostics, tuning, lubrication, cooling, exhaust.
Fuel System:
Carburetor identification, adjustment, cleaning, fuel tank, fuel lines, petcock.
Transmission System:
Gearbox operation, clutch, shift mechanism, lubrication, repair procedures.
Chassis Frame:
Frame inspection, alignment, swingarm, pivot bearings, steering head bearings.
Suspension Front:
Front fork disassembly, assembly, oil change, seal replacement, spring rates.
Brakes Front:
Disc brake caliper servicing, hydraulic lines, master cylinder, pad replacement, bleeding.
Electrical System:
Ignition system, lighting, charging system (stator, regulator/rectifier), battery, wiring diagrams.
Cooling System:
Air cooling (fins), component checks.
Exhaust System:
Muffler, pipe inspection, sealing.
Wheels Tires:
Wheel bearing maintenance, spoke tensioning, tire pressure specifications.
Bodywork Plastics:
Fairing, fenders, seat, fuel tank removal and installation.
Rear Shock ABSorber:
Monoshock unit service, linkage maintenance, damping adjustments.
Rear Brake System:
Drum brake inspection, adjustment, shoe replacement.
Routine Maintenance:
Oil changes, filter replacements, chain adjustment, spark plug checks, air filter cleaning.
Engine Rebuild:
Top-end overhaul, piston, rings, cylinder, crankshaft service.
Carburetor Tuning:
Jetting, idle speed, mixture adjustments for optimal performance.
Troubleshooting Diagnostics:
Systematic fault finding for common and complex issues.
Wiring Diagrams:
Detailed electrical schematics for accurate diagnosis and repair.
Component Disassembly Assembly:
Step-by-step guides for all major motorcycle components.
Diagnostic Capability:
Advanced diagnostics and troubleshooting for intricate issues.
Repair Complexity:
Covers everything from basic adjustments to complete engine and chassis overhauls.
Completeness:
Full factory specification for comprehensive repair and maintenance.
Engine Type:
Two-Stroke, Single-Cylinder
Displacement:
123 cc (7.5 cubic inches)
Bore X Stroke:
56.4 mm x 50.0 mm (approximate)
Compression Ratio:
Approx. 7.2:1 (varies slightly by model revision)
Cooling System:
Forced Air Cooling
Ignition System:
CDI (Capacitor Discharge Ignition)
Spark Plug Type:
NGK B8ES (or equivalent, consult manual for specific)
Horsepower Estimated:
Approx. 17-20 HP (at crankshaft, varies by market and tuning)
Torque Estimated:
Approx. 14-16 Nm (at crankshaft, varies by market and tuning)
Carburetor Model:
Mikuni VM26SS (typical for this era)
Fuel Type:
Unleaded Gasoline (min. 91 RON / 87 AKI recommended)
Oil Mixture Ratio:
50:1 (2-stroke oil to gasoline in the oil injection system)
Engine Oil Change:
Refer to manual; typically every 2,000-3,000 km or annually. Crankcase oil change is crucial.
Air Filter Cleaning:
Check and clean every 1,000-2,000 km, especially in dusty conditions.
Chain Lubrication Adjustment:
Lubricate every 500 km, adjust tension as needed according to manual specifications.
Spark Plug Service:
Inspect and clean/gap every 3,000-4,000 km, replace as necessary.
Transmission Oil Type:
Yamaha Gear Oil 10W-30 (or equivalent API GL-4 specification)
Fork Oil Type:
Yamaha Fork Oil G10 (or equivalent SAE 10W)
Brake Fluid Type:
DOT 3 or DOT 4 Hydraulic Brake Fluid
Common Wear Items:
Piston rings, crankshaft seals, clutch plates, and suspension seals are common wear items on high-mileage units.
Carburetor Performance:
Carburetors can be sensitive to altitude and air filter condition; regular cleaning and tuning are beneficial.
Electrical Reliability:
Older wiring harnesses can develop corrosion or damage, affecting ignition or charging systems. Manual is key for troubleshooting.
Yamaha Motorcycle Legacy:
Yamaha has a long history of producing reliable and performance-oriented motorcycles, particularly in the off-road and dual-sport categories.
Dt Series Development:
The DT series originated in the late 1960s and evolved through various displacements and configurations, emphasizing versatility and durability.
Manufacturing Location Typical:
Japan (primary manufacturing hub for Yamaha at this time)
Dt125R Production Span:
Covered years 1987-1988, part of a continuous DT125 lineage.
