Yamaha QT50/MA50 & QT50J 1979–1992 Manual Set (P/N LIT-11626-02-97)

The service manual provides the workshop repair procedures, while the owner’s manual explains QT50J operation, routine checks and maintenance schedules. The separate schematic provides a larger version of the owner’s wiring diagram.

Workshop teardown and repair coverage belongs to the QT50/MA50 service publication. The QT50J file is an owner’s manual, not a later service supplement.

PDF Search, Bookmarks and Wiring Readability

Text search and diagram detail: Technical content is not searchable in any of the three PDFs. The service manual has chapter and subsection bookmarks; the owner’s manual and separate schematic have none. Small wiring labels require zooming, and some labels in the owner’s diagram remain soft when enlarged.

The ZIP contains three printable PDFs totaling 169 pages. These totals include four cover pages across the two manuals, their contents and section-divider pages, and three memo pages.

Two-Stroke Overhaul, Autolube Testing and Shaft-Drive Repair

The selected coverage highlights below outline the main workshop material. Other topics include headlight-beam adjustment and battery-storage guidance.

• Engine overhaul: Step-by-step procedures for engine removal, disassembly, cylinder and piston inspection, crankshaft service, crankcase assembly, adjustment and installation.

• Carburetion and Autolube: Carburetor inspection and repair, reed-valve checks, air-cleaner servicing, oil-pump bleeding, cable adjustment, delivery-line troubleshooting and pump-output testing.

• Transmission and shaft drive: Clutch and kick-starter inspection, transmission assembly, drive-housing removal, gear inspection, bearing checks and ring-gear deflection measurement.

• Brakes and chassis: Drum-brake service, wheel-bearing replacement, front-fork disassembly and reassembly, steering-head inspection, throttle maintenance and cable-junction servicing.

• Electrical diagnosis: CDI ignition checks, magneto charge-coil and pulser-coil tests, ignition-coil testing, charging-circuit diagnosis, rectifier checks and AC/DC lighting fault tracing.

• Drawings and service data: Exploded assemblies, cable-routing views, regional wiring diagrams, torque tables, component wear limits, fluid capacities and electrical test specifications.

The workshop manual was written for authorized Yamaha dealers and qualified mechanics who already understand basic mechanical procedures; the owner’s volume explains operation and basic inspection items.

QT50J Controls and Owner Reference

The owner’s manual covers safety labels, vehicle identification, control functions, starting and riding, engine break-in and daily pre-operation checks. Periodic maintenance and lubrication charts sit alongside specifications, stopping-distance information and the original warranty-information section.

Engine Inspection and Reassembly

The service chapters cover the cylinder head and cylinder, piston and rings, crankshaft, crankcase, bearings and oil seals. Inspection material distinguishes component wear, running clearances, crankshaft runout and bearing condition, supporting decisions about honing, oversize pistons and parts replacement.

Exploded views identify the clutch, primary drive and kick-starter components. Reassembly material addresses shaft seating, shims, piston orientation and assembly-specific tightening requirements.

The crankshaft-installation cautions address scratches to the shaft and damage to the oil-seal lips.

Carburetor, Reed Valve and Autolube Diagnosis

Carburetor coverage centers on the Mikuni VM12SC. Inspection procedures address the float, needle valve, jets, throttle slide, jet needle, pilot-air screw and internal passages. Reed-petal condition, seating, leakage and stopper clearance receive separate attention.

Autolube troubleshooting checks delivery-line restrictions, routing, seals and loose fittings before proceeding to measured pump-output testing. That sequence helps distinguish an oil-delivery problem from a pump that requires replacement.

The air-cleaner section warns that running without the foam element can alter carburetor jetting and admit unfiltered air, causing rapid wear, overheating or engine damage.

Shaft Drive, Wheels and Steering

The shaft-drive section documents rear-arm and drive-housing removal, with exploded views identifying the drive pinion, ring gear, bearings, spacers, shims and seals. Inspection includes gear-tooth condition and ring-gear deflection, followed by lubrication and housing-installation requirements.

Chassis procedures cover both wheels, axles, brake shoes, drums and shoe plates. Front-fork and steering-head sections address inner-tube condition, retaining clips, bearing balls and races; cable material includes the throttle-to-Autolube junction.

Ignition Tests and Regional Wiring

The electrical chapter explains CDI operation and provides spark-gap, coil-resistance, charging-output and silicon-rectifier tests. Separate AC and DC circuit checks address lighting, signals, the horn and oil-warning circuit.

Drawings include the CDI operating circuit, charging-output graph, oil-warning circuit, cable-routing layouts and full wiring schematics. Regional drawings labeled “Except for Australia and New Zealand” distinguish the relevant wiring and cable arrangements. The owner’s manual adds a component-labeled schematic and wire-color key.

Service equipment: Listed tools include flywheel puller 90890-01189, crankcase separator 90890-01135 and crank installer components 90890-01274, 90890-01275 and 90890-01278. Electrotester 90890-03021 is specified for ignition testing.

Fuel-system work, rotating-engine tests, brake repair and road testing require suitable ventilation, fire precautions, stable machine support and the manual’s workshop safety guidance.

Examples of Piston Clearance and Shaft-Drive Limits

For the QT50/MA50 engine, the piston-inspection table specifies a normal piston-to-cylinder clearance of 0.035–0.047 mm and a maximum wear limit of 0.07 mm for evaluating piston and cylinder condition.

The shaft-drive inspection section gives a ring-gear assembly deflection limit of 0.08 mm (0.0031 in), accompanied by a dial-gauge measurement drawing.