Yamaha 80–175cc Piston-Port Clymer Service & Repair Manual (1968–1976)

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

Reading the PDF and Wiring Diagrams

Text search and diagram detail: The PDF has no text search or built-in bookmarks. The table of contents and index provide page references. The early and late lighting diagrams are sideways in the file, and some fine labels and lines in the AT1-type charging diagram remain faint at higher zoom.

The English download is one printable PDF with 196 pages. That total includes six opening pages with the title, chapter guide, contents, and quick-reference tables, followed by 186 numbered pages, one notes page, and three wiring-diagram pages.

Two-Stroke Repair, Chassis Service, and Electrical Tests

These are selected topics from the manual. The book also shows how to check cylinder compression and inspect the reed-valve assembly.

• Engine repair: Periodic tune-up, engine removal, top-end inspection, crankcase separation, and crankshaft overhaul, with checks for pistons, rings, bearings, and seals.
• Clutch and transmission: Wet-clutch service, kickstarter and shifter repairs, gear and shaft inspection, and transmission end-play adjustment, with exploded views of different designs.
• Fuel and lubrication: Mikuni carburetor overhaul, float-level adjustment, mixture troubleshooting, and Autolube pump bleeding and cable adjustment.
• Electrical systems: Breaker-point and CDI timing, flywheel magneto diagnosis, starter/generator testing, and separate early and late lighting and charging diagrams.
• Chassis service: Wheel bearings, drum brakes, front forks, steering-head bearings, rear suspension, and drive-chain inspection and adjustment.
• 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. Crankshaft rebuilding calls for an equipped shop with a press and alignment fixtures.

Engine, Transmission, and Clutch Repair

Drawings explain the intake, compression, power, and exhaust phases of piston-port and reed-valve engines. The top-end section pairs inspection procedures with piston-clearance and ring-fit tables, including separate entries for selected MX, YZ, and 125cc GYT-kit applications.

The manual matches wet-clutch designs, kickstarters, and shifters to specific models. It gives step-by-step procedures for separating the crankcases and checking transmission shaft end play. Prying the case halves apart can damage the sealing faces. The transmission repair chapter illustrates four- and five-speed designs. The YZ100C appendix entry provides six-speed gear ratios.

Carburetors and Autolube

Separate exploded views show the Mikuni single-unit and independent-float designs. The carburetor adjustment summary links throttle opening to the relevant metering components, helping narrow down a hesitation or mixture problem before changing jets.

The appendix identifies Teikei Y16P-3 carburetors on GT models and distinguishes early GTMX settings by engine number. Autolube coverage includes pump removal, oil-delivery checks, and air bleeding. The YZ125A specification lists premix lubrication.

Ignition, Charging, and Fault Diagnosis

The electrical chapter describes tests for ignition coils, condensers, rectifiers, generator output, brushes, armatures, and voltage regulators. Alongside the early and late lighting diagrams are the AT1-type charging circuit and CDI wiring diagrams. Troubleshooting tables link starting trouble, power loss, clutch slip or drag, shifting problems, and poor handling to likely causes.

Chassis and Off-Road Setup

Chassis procedures include wheel-bearing replacement, rear-hub cushion inspection, brake-shoe wear checks, fork seal service, and swingarm bushing replacement. Monocross coverage includes unit removal, inspection, and spring replacement. The manual warns against opening the nitrogen-pressurized damper.

The performance chapter discusses gearing, wheel and spring rates, exhaust changes, reed-valve conversions, and port layouts. It explains how setup choices affect low-speed torque and peak power. Use adequate ventilation and eye protection during solvent cleaning and press work.

Crankshaft and Charging Test Examples

The crankshaft inspection section gives a standard runout limit of 0.0012 in (0.03 mm) at the main bearing journals and a repair limit of 0.004 in (0.10 mm) for all covered models.

For early-model charging circuits, the output table specifies at least 5.0 V DC at 2,500 rpm and no more than 8.0 V DC at 8,000 rpm, with the lights on and a fully charged battery in good condition.