Yamaha YFM80N ATV Service Manual 1985–1988 (P/N LIT-11616-04-84)

Yamaha’s factory service manual for the YFM80N, model code 55X, covers routine maintenance and powertrain, chassis, carburetor, and electrical repair. P/N LIT-11616-04-84 identifies the first edition dated September 1984, supplied here in its third printing dated April 1986.

PDF Access, Diagram Detail, and Page Count

Search, navigation, and wiring detail: PDF text search is unavailable, and there are no embedded PDF bookmarks. Small wire-color codes and connector labels in the wiring diagrams require zooming for comfortable reading.

One printable English PDF contains 179 pages, including the cover, publication details, introductory material, one additional front-matter page, and three blank divider pages. Individual sections can be printed for use at the workbench.

Engine Overhaul, Shaft Drive, and Electrical Fault Tracing

The following selected coverage highlights summarize the main workshop areas rather than reproduce the full contents. Other topics include speed-limiter adjustment and fuel-cock cleaning.

• Maintenance and adjustment: Cam-chain tension, valve clearance, compression testing, clutch adjustment, oil-strainer cleaning, and the periodic maintenance and lubrication schedule.

• Engine overhaul: Step-by-step procedures for engine removal and remounting, cylinder-head service, crankcase separation, piston inspection, and crankshaft assessment.

• Clutch and transmission: Wet centrifugal clutch disassembly, plate inspection and assembly-height adjustment, transmission inspection, shift-component checks, and middle-gear shim selection.

• Carburetor repair: VM16SH Mikuni removal, disassembly, inspection, reassembly, fuel-level adjustment, and float-height measurement, supported by a sectional view.

• Chassis and shaft drive: Wheel-bearing replacement, rear drum-brake service, steering-shaft and tie-rod work, toe-in adjustment, rear-axle inspection, and shaft-drive disassembly.

• Electrical diagnosis: Master and system-specific wiring diagrams, troubleshooting charts, starter-motor inspection, relay tests, charging checks, and CDI ignition fault isolation.

Yamaha wrote this manual primarily for its dealers and qualified mechanics, assuming a working understanding of mechanical repair concepts and procedures.

Internal Engine, Clutch, and Transmission Work

The engine chapter extends from top-end disassembly into rocker arms and shafts, camshaft, cam chain and tensioner, valves and guides, piston rings, oil pump, CDI magneto, and internal transmission components. Valve-guide replacement, valve-seat cutting and lapping, and cylinder and piston measurements are described alongside the inspection limits used to assess whether parts can be reused.

Assembly references: Crankshaft and transmission assembly views identify component relationships. Clutch procedures distinguish the black and silver friction plates and bent clutch plate, with separate checks for clutch-boss height and friction-plate height.

Middle-gear service includes U-joint work and measured shim selection. Yamaha notes that displaced needle rollers can prevent the yoke from seating correctly; forcing that assembly risks bearing damage.

Rear Brake, Steering, and Final Drive

The rear-brake exploded view supports shoe, drum, camshaft, seal, and bearing service. Inspection data addresses lining wear, rear-axle runout, and bearing condition, while the reassembly section covers the final-gear housing and its specified grease.

Steering coverage separates shaft and bushing inspection from knuckle and tie-rod work. Tie-rod identification, assembly-length adjustment, and toe-in checks provide the references needed after steering components have been replaced.

The shaft-drive assembly view accompanies removal, component inspection, and reinstallation procedures. Wheel-bearing instructions also identify a specific damage risk: installation loads through the inner race or balls can damage the bearing.

Mikuni Carburetion and Circuit Diagnosis

The VM16SH carburetor section identifies the #80 main jet, 3HP9 jet needle, and #12.5 pilot jet. Its sectional view distinguishes air, fuel, and mixture passages, while the adjustment procedures explain the different references used for fuel level and float height.

Fault isolation: Separate charts address a starter that will not operate, charging-system faults, and absent or intermittent ignition spark. Supporting tests cover the starter motor and brushes, starter relay, starting circuit cut-off relay, charging output and coil resistance, ignition spark gap, ignition coil, pick-up coil, and source coil.

These charts connect symptoms with component checks, helping the mechanic narrow a fault before selecting replacement parts. Lubrication diagrams and cable-routing drawings add references for oil circulation, harness placement, and breather routing.

Tools and Workshop References

The tool list supports repair planning by identifying equipment beyond ordinary hand tools. Examples include the YU-33223 Compression Gauge, YM-01312 Fuel Level Gauge, and YU-03112 Pocket Tester for measurement and diagnosis.

Mechanical service references include the YM-91042 Clutch Holder, YU-01135 Crankcase Separating Tool, and YU-33975 Ring Nut Wrench. The appendices provide component-specific torque tables, general torque specifications, maintenance data, and unit-conversion tables.

ATV repair in this manual includes rotating engine parts, battery and ignition circuits, brake components, and work that requires the machine to be securely supported. Use appropriate protective equipment and proper support before service, and have safety-critical brake, steering, or electrical work checked by a qualified technician when necessary.

Selected Carburetor Settings and Ignition-Coil Test Values

For the VM16SH carburetor, the specified fuel level is 3.5 ± 1.0 mm below the carburetor-body edge. Float height is 21.0 ± 0.5 mm, measured from the float-chamber mating surface with the gasket removed and the needle valve uncompressed.

Ignition-coil testing specifies 1.6 Ω ±10% for the primary winding and 6.6 kΩ ±20% for the secondary winding, both at 20°C (68°F). The accompanying illustrations show the corresponding tester connections.