Yamaha YFA1 / YFM125S ATV Service Manual Set, 1989–2007 (P/N 3FA-28197-10)

Use the supplements alongside the base repair chapters. The YFM125S lighting diagnosis refers back to battery and lighting procedures in the base manual and switch checks in the YFA1P/YFA1PC supplement.

Coverage limit: The base manual’s reverse-indicator troubleshooting chart ends after the shift-lever-switch check; its continuation is not included.

Search Coverage, Bookmarks, and Wiring Detail

Text search and navigation: PDF text search is available on pages 1–53; the remaining sections have no searchable text layer. Chapter and section bookmarks are included. Small wiring labels require zooming.

A single printable 309-page PDF contains all four publications listed above, including their introductory and contents pages and four memo pages.

Engine Overhaul, V-Belt Drive, and Electrical Diagnosis

These selected content highlights are a preview rather than a complete table of contents. Other topics include spark arrester cleaning and headlight-beam adjustment.

• Engine overhaul: Step-by-step engine removal, crankcase separation, cylinder-head repair, valve and piston inspection, and reassembly with timing references and torque specifications.

• V-belt drive and transmission: Primary and secondary sheave service, centrifugal clutch inspection, starter-clutch checks, and internal transmission and shifter repair.

• Fuel system: Mikuni VM18SH carburetor disassembly, inspection, reassembly, float-height adjustment, and fuel-level checks.

• Brakes and chassis: Drum-brake service, wheel and axle inspection, steering-knuckle and swingarm work, toe-in adjustment, and drive-chain service.

• Electrical diagnosis: Ignition, electric-starting, charging, lighting, and signal-system test charts, including starter-motor inspection and switch-continuity checks.

• Service references: Maintenance schedules, lubrication charts, cable-routing diagrams, exploded assemblies, job instruction charts, and component-specific specifications.

This set is suited to mechanics who can use workshop measuring equipment and the specified special tools.

Engine Inspection and Assembly References

The overhaul chapter covers the crankshaft and balancer, camshaft and rocker arms, valve guides and seats, oil pump, and electric starter drive. Component-specific dimensions and wear limits let you assess parts during teardown against the documented repair or replacement criteria.

Timing and lubrication: The timing chain uses an automatic tensioner; assembly instructions cover its installation and the camshaft and balancer alignment marks. The Lubrication Diagram maps the oil circuit, while lubrication tables identify the required lubricants at assembly points.

Clutch and Internal Transmission Work

The secondary-sheave procedures identify spring holder 90890-01337, a sheave holder, and a locknut wrench for clutch disassembly and assembly. Internal transmission inspection extends to the shift fork, guide bar, gear teeth, engagement dogs, and shaft runout.

Carburetor Settings and Supplement Differences

The carburetor Sectional View identifies air, fuel, and mixture passages. Supplement tables distinguish California carburetor identification marks and jetting from other versions, so the base carburetor settings should not be treated as universal.

Steering, Rear Hubs, and Suspension

The base drawings show the steering column and handlebar holder; the YFA1P/YFA1PC supplement adds the cable-joint layout. Rear-hub coverage includes bearing and oil-seal replacement and the staged rear-axle-nut tightening procedure.

The rear-axle removal notes warn that direct hammer blows can damage the axle threads and splines. Support the ATV securely during wheel or suspension work and use appropriate shop PPE.

Wiring Diagrams and Fault Isolation

Full-page wiring diagrams for YFM125S, YFA1P/YFA1PC, and YFA1(W) show wire colors and connector layouts. The Electric Starting System circuit diagram and diagnostic charts provide separate checks for the battery, starter motor, relays, neutral switch, and wiring.

Charging and lighting diagnosis includes A.C. magneto coil measurements. Signal-system checks address lamp, socket, and switch faults.

Cylinder-Head, Sheave, and Generator Data Samples

The YFA1(W) base manual lists 22 Nm for the M8 cylinder-head bolts and 55 Nm for the primary fixed-sheave nut. Cold intake valve clearance is 0.08–0.12 mm. The cylinder-head assembly instructions distinguish fasteners by size rather than assigning one torque to the entire assembly.

The YFM125S supplement lists standard generator output as 14 V, 150 W at 5,000 r/min and battery capacity as 12 V, 12 Ah.