Yamaha YFM350ER Moto-4 ATV Service Manual Set, 1987–1990

The supplements update the base manual with model-specific service information and specifications. Use the base procedures alongside the applicable supplement, particularly for electrical tests, brake adjustments, and rear axle assembly.

Printable PDF, Bookmarks, and Wiring Detail

Text search and diagram detail: Manual text is not searchable. Embedded bookmarks provide navigation through the base manual and supplements, while small wire-color and connector labels in the wiring diagrams require zooming.

One printable English-language PDF totals 310 pages, including three blank pages and three memo pages within the publication counts above.

Engine Overhaul, Shaft Drive, and Electrical Diagnosis

These selected service topics illustrate the repair coverage rather than reproduce the full contents. Other subjects include fuel-cock cleaning and headlight beam adjustment.

• Engine repair: Engine removal and installation, top-end overhaul, crankcase separation, recoil starter rebuilds, and internal component inspection.

• Clutch and transmission: Primary and secondary clutch inspection, transmission main axle teardown, shift mechanism service, and assembly checks.

• Fuel and lubrication: Carburetor disassembly, fuel-level adjustment, oil pump inspection, and engine and final gear lubricant specifications.

• Shaft drive and chassis: Middle and final gear service, drive shaft inspection, steering repair, suspension service, and brake adjustment.

• Electrical diagnosis: CDI ignition, electric starting, charging-system tests, electrical troubleshooting charts, and model-specific wiring diagrams.

Suited to mechanics and experienced owners familiar with internal engine repair, precision measurements, and the special tools required for crankshaft and gear service.

Engine Repair and Maintenance

The engine is an air-cooled, single-cylinder SOHC four-stroke with an oil cooler. Lubrication diagrams show the oil circuit and cooler connections.

Step-by-step top-end procedures cover rocker arm shaft extraction, valve seat recutting, and decompression cam inspection. Valve seat cutting schematics and crankshaft assembly views accompany the component instructions.

Timing and assembly: The engine chapter details CDI rotor removal and installation, balancer drive gear servicing, and punch-mark alignment with the buffer boss. Automatic cam chain tensioner inspection, valve clearance adjustment, and compression pressure testing are also covered. Component-specific torque tables distinguish the cylinder head fasteners.

Carburetor and Oil System Service

Fuel system coverage includes carburetor float level settings, throttle cable adjustment, and air filter maintenance. The Mikuni BTM32SH carburetor sectional view shows the internal component arrangement, including the metering, starter, and float systems.

Oil pump clearances and fluid-capacity tables support lubrication-system service. The YFM350ERT oil-change quantity differs between the maintenance instructions and specification tables.

Clutch, Transmission, and Shaft Drive Repair

Clutch service extends to friction plates, springs, and the secondary clutch, while the shift mechanism section documents shift cam segment alignment. The ERU supplement provides revised high-range transmission ratios.

Middle driven gear lash measurement and shim selection receive dedicated coverage. The Shaft Drive Troubleshooting chart relates driveline symptoms to possible bearing, gear, and drive shaft faults.

The middle gear instructions warn that overtightening the bearing housing bolts can reduce gear lash and damage the gears.

Steering, Brakes, and Rear Axle

The chassis section covers steering shaft bushings, tie-rod inspection, toe-in adjustment, wheel bearings, and swingarm checks. Rear brake coverage extends to caliper disassembly, pad inspection, and disc thickness and deflection measurements.

The ERW supplement adds revised front brake service and rear axle nut procedures, including use of rear axle nut wrench YM-37132. The rear axle instructions identify direct hammer blows as a cause of thread and spline damage.

The ERA supplement updates front brake and rear brake lever and pedal adjustments, including checks for brake drag.

Ignition, Starting, and Model-Specific Electrical Tests

Electrical troubleshooting covers magneto pick-up coil resistance, fuse ratings, ignition timing verification, and starter motor inspection. Cable routing drawings and the starting-circuit cut-off schematic accompany the wiring diagrams. Lighting, neutral and reverse indicators, and the auxiliary DC terminal have separate diagnostic coverage.

The ERU supplement adds oil temperature warning circuit diagnosis, including thermo relay tests and thermo switch fault isolation. The ERA supplement supplies revised CDI, ignition coil, and charging-system specifications; these distinctions help match electrical tests to the installed components.

Before turning wrenches on the engine, brakes, or shaft drive, ensure you have the proper tools and mechanical background to work safely; improper maintenance can cause equipment damage or injury.

Preview of Clutch Spring and Friction Plate Limits

The YFM350ERT clutch inspection section lists a minimum clutch spring length of 45.8 mm, compared with 46.5 mm in the YFM350ERA supplement. Both list a clutch friction plate wear limit of 2.8 mm.

Together with the valve spring free-length limits, these specifications help you assess which parts can be reused before reassembly.