1968–1976 Yamaha 80–175cc Clymer Service & Repair Manual

This Clymer service and repair manual covers 1968–1976 Yamaha 80–175cc single-cylinder two-strokes, including AT, DT, CT, MX, YZ and GT variants with piston-port or reed-valve induction.

• Engine repair: Periodic tune-up, engine removal, top-end inspection, crankcase separation and crankshaft overhaul, with piston, ring, bearing and seal checks.

• Clutch and transmission: Wet-clutch service, kickstarter and shifter repairs, transmission inspection and shaft end-play adjustment, supported by variant-specific exploded views.

• Fuel and lubrication: Mikuni carburetor overhaul, float-level adjustment, mixture troubleshooting, and Autolube pump inspection, bleeding and cable adjustment.

• Electrical systems: Breaker-point and CDI timing, flywheel magneto diagnosis, starter/generator testing, and separate early- and late-type lighting and charging diagrams.

• Chassis service: Wheels, drum brakes, front forks, steering-head bearings, rear suspension and drive chain, with removal, inspection and adjustment procedures.

• Troubleshooting and tuning: Symptom-based fault checks and a separate off-road performance chapter covering gearing, suspension setup, exhaust changes and cylinder porting.

Written for Yamaha owners, the book supports routine service by readers comfortable with tools, while crankshaft rebuilding requires a properly equipped shop and considerable experience.

Engine, Transmission, and Clutch Repair

Operating-principle illustrations explain the intake, compression, power and exhaust phases of piston-port and reed-valve engines. Cylinder inspection and piston service are supported by clearance and ring-fit tables, with separate entries for MX, YZ and 125cc GYT-kit applications.

Four clutch types and several kickstarter and shifter arrangements are matched to specific models. The transmission repair chapter illustrates four- and five-speed designs; the YZ100C specification sheet separately lists six-speed ratios.

Crankshaft work includes press disassembly, bearing-clearance checks, runout measurement and dial-indicator alignment. The crankcase section warns that prying the halves apart can damage sealing faces and cause oil leaks.

Carburetors and Autolube

Separate exploded views show the Mikuni single-unit and independent-float designs. The Carburetor Adjustment Summary connects throttle-opening ranges to the relevant metering components, helping narrow down a hesitation or mixture problem before changing jets.

The appendix also identifies Teikei Y16P-3 carburetors on GT models and distinguishes GTMX settings before engine No. 2793. The carburetor chapter flags the risk of float-needle valve damage when compressed air is applied to an assembled carburetor.

Autolube coverage includes pump removal and installation, delivery-line checks and air bleeding. Lubrication specifications distinguish oil-injected models from the premix YZ125A.

Ignition, Charging, and Fault Diagnosis

Electrical testing covers ignition-coil resistance, condenser capacitance and insulation, rectifier checks, generator output, brushes, armature condition and voltage-regulator operation. The AT1-Type Charging System Circuit and CDI Wiring diagrams accompany the system descriptions.

Earlier Type Lighting/Charging System and Later Type Lighting/Charging System diagrams show the circuit differences. Separate charging tests account for the different systems and operating conditions.

Troubleshooting tables address starting difficulties, power loss, clutch slip or drag, shifting problems and poor handling. These sections connect symptoms with likely causes and the relevant inspection areas.

Chassis and Performance Work

Chassis procedures cover wheel-bearing replacement, rear-hub cushions, brake-shoe wear checks, fork seals and swingarm bushings. Monocross coverage includes unit removal, installation, inspection and spring replacement; the manual warns against dismantling the nitrogen-pressurized damper.

The performance chapter discusses off-road gearing choices, wheel and spring rates, exhaust changes, reed-valve conversions and cylinder-port layouts. It distinguishes changes aimed at low-speed torque from those intended for peak power.

Reference material includes cylinder-head, flywheel and axle tightening torques, fluid capacities, wear limits and electrical test specifications. Use adequate ventilation and eye protection during solvent cleaning and press work.