Yamaha YFM250 Moto 4 ATV 1989–1991 Service Manual (P/N LIT-11616-06–62 / LIT-11616-YF-25)

• Official Yamaha factory publication, 330-page PDF set: one-page Yamaha outer cover carrying LIT-11616-YF-25, the 308-page YFM250W Service Manual LIT-11616-06-62 (1st edition, August 1988), and the 21-page YFM250A Supplementary Service Manual LIT-11616-07-96 (1st edition, June 1989).
• 3GH model coverage: YFM250W engine starting numbers are 3GH-000101 for the U.S. and 3GH-047101 for Canada, Switzerland, Great Britain, France, Australia, New Zealand, and South Africa. YFM250A engine starts are 3GH-064101 for the U.S., Australia, New Zealand, and South Africa, or 3GH-084101 for Canada, Switzerland, Great Britain, and France; matching VIN and frame-identification data is included.
• Routine service procedures: includes the factory maintenance schedule, valve-clearance and ignition-timing checks, compression testing, clutch and drive-select adjustment, carburetor service, final-drive oil service, brake adjustment, toe-in setup, shock preload, battery inspection, and cable routing.
• Engine overhaul and repair: covers removal and remounting, cylinder-head and valve work, camshaft and timing-chain service, cylinder and piston inspection, crankcase separation, crankshaft and balancer service, oil-pump inspection, CDI magneto removal, and recoil-starter work for applicable non-U.S. machines.
• Transmission and shaft-drive repair: details the wet automatic centrifugal clutch, primary and secondary clutches, constant-mesh five-speed transmission, high/low/reverse sub-transmission, universal joint, drive shaft, final drive, shim selection, and gear-lash measurement and adjustment.
• Chassis repair: provides removal, inspection, and installation procedures for the front drum brakes, rear disc brake, rear axle, steering shaft and tie rods, front arms, steering knuckles, shock absorbers, swingarm, wheel bearings, and related seals and bushings.
• Electrical diagnosis: supplies the complete YFM250W circuit diagram, switch-connection charts, component test data, and fault-isolation procedures for CDI ignition, electric starting and its safety interlocks, starter motor, charging, lighting, and neutral/reverse indicator circuits.

This is Yamaha factory shop literature written primarily for Yamaha dealers and qualified mechanics. It assumes a basic understanding of machine repair, making it suited to technicians and experienced ATV mechanics who are comfortable with precision measurement, puller and press work, and electrical testing.

Engine and Drivetrain Service

The base manual identifies the YFM250W's air-cooled 229.6cc single-cylinder SOHC four-stroke and wet-sump lubrication system. U.S. machines use electric starting; the other listed market versions also have a recoil starter. Exploded assembly drawings precede the major disassembly sections, and the procedures carry each system through removal, teardown, inspection, repair, assembly, adjustment, and operational checks.

Engine data covers torque, lubrication, and capacity tables plus inspection limits for the valve train, cylinder and piston, crankshaft, clutches, oil pump, and transmission. Drivetrain work goes beyond parts replacement: the manual gives factory calculations for drive-pinion, driven-pinion, final-drive, and ring-gear shim selection, followed by final gear-lash measurement and correction. A symptom chart separates wheel-bearing noise, incorrect gear lash, damaged gear teeth, universal-joint faults, and lubrication-related seizure.

YFM250A Supplement and Scope

The YFM250A supplement is designed to be used with the YFM250W base manual. It adds the later machine-identification data, revised general and piston-ring specifications, updated cable-routing views, front and rear brake adjustments, tire data, shift-lever removal and setup, and revised sub-transmission removal and installation. Coverage in this PDF is specific to the YFM250W base model and the YFM250A changes; it does not contain a separate YFM250B or 1991 model-change supplement.

Chassis, Electrical, and Diagnostic Data

Chassis tables cover brake wear limits, wheel and axle runout, suspension and swingarm inspection limits, fastener torques, approved lubricants, and sealing points. Named visual references include the YFM250W circuit diagram, carburetor sectional view, engine lubrication diagrams, and separate ignition, electric-starting, and charging-system circuits. The electrical chapter pairs those schematics with switch-terminal continuity charts, resistance and output specifications, starter-relay and starter-motor tests, and diagnostic paths for no-spark, no-crank, no-charge, lighting, and indicator faults.

The final troubleshooting chapter also covers hard starting, poor idle or high-speed operation, difficult or jumping shifts, clutch slip or drag, overheating, poor braking, shock-absorber faults, unstable handling, and dim or failed lighting. These charts point back to the applicable inspection and repair sections instead of treating symptoms as isolated adjustments.

Special Tools and Repair Cautions

Factory tool callouts include the crankcase separating tool YU-01135/90890-01135, flywheel puller YU-33270/90890-01362 with adapter YM-04087/90890-04087, gear-lash tool YM-01231/90890-01231, and rear-axle nut wrench YM-37132/90890-01419. Additional listings cover valve-guide service, clutch holding, universal-joint work, fuel-level measurement, and ignition/electrical testing.

The manual warns against forcing uneven crankcase separation or striking the gasket surfaces, and against hammering directly on the rear axle because its threads and splines can be damaged. Securely support the ATV before rear-drive, swingarm, or suspension removal, and follow the factory brake, battery, and starter-circuit safety instructions before beginning repair work.