1968-1976 Yamaha 80-175cc Piston-Port Service Manual (OEM)
Yamaha Models Covered & Key Technical Specifications
Models: Yamaha AT1, AT2, DT100, DT125, DT175, CT1, CT2, CT3, MX100, MX125, MX175, YZ80, YZ100, YZ125, GT1, GT80, GTMX
Sub-models / Variants: 80cc, 90cc, 100cc, 125cc, 175cc, Enduro, Motocross (MX), GYT Kit
Model Years: 1968–1976
Technical Data:
- Engine type: 2-stroke single cylinder, piston-port, dual shock suspension
- Breaker point gap: 0.012–0.016 in (0.3–0.4 mm)
- Spark plug gap: 0.016–0.020 in (0.4–0.5 mm) for MX models; 0.020–0.023 in (0.5–0.6 mm) for others
- Cylinder head nut torque: 7.3 ft-lb (1.0 kg-m) for 80cc; 14.5 ft-lb (2.0 kg-m) for others
- Idle speed: 900–1,000 rpm (80–100cc); 1,000–1,200 rpm (125–175cc)
- Piston ring gap (80–100cc): 0.006–0.014 in (0.15–0.33 mm)
- Transmission oil capacity: 0.4–0.7 U.S. qt (0.5–0.75 liters) depending on model
Yamaha Manual Features & Content Preview
- Covers 1968–1976 Yamaha 80cc through 175cc piston-port motorcycles, including AT, DT, CT, MX, and YZ variants
- Original OEM manufacturer publication detailing revisions and technical specifications for the production era
- Contains 91 diagrams, 10 maintenance schedule tables, and comprehensive wiring schematics for early and late lighting systems
- Serves as the definitive reference for piston-port engine maintenance, documenting critical assembly, tuning, and timing data
Engine, Transmission, and Clutch Documentation
Inside, mechanics will find an extensive breakdown of Yamaha's two-stroke operating principles. The text clearly maps out intake, compression, power, and exhaust strokes specific to piston-port engines. It outlines every critical internal component. You get exact views of the crankshaft, pistons, reed valves, and the Autolube system. For lower-end work, the transmission section details shifting mechanisms, gear ratios, and bearing maintenance across both four- and five-speed setups.
Factory assembly requires precision. Because of this, the guide logs exact tightening torques for cylinder heads, flywheels, and axle nuts. Piston clearance is documented precisely at 0.0014 to 0.0020 inches, varying slightly by displacement and exact model variant. If you are rebuilding a top end, you will find 175cc engine piston ring side clearances specified strictly at 0.0012 to 0.0020 inches within the data tables. Proper shop safety protocols should always be observed when tearing down these vintage engines to avoid injury or component damage.
Carburetor and Electrical Systems
Fuel delivery and spark are critical on vintage two-strokes. The carburetor service chapters cover both Mikuni single and independent float types. They provide exact float level adjustments and jetting summaries across different throttle ranges. On the electrical side, the manual features complete circuit diagrams for the flywheel magneto ignition and early lighting systems.
Diagnostic baselines are clearly laid out for troubleshooting. Magneto ignition coil resistance sits at approximately 0.5 ohm. Condenser capacity is rated between 0.18 and 0.25 mfd. For early models, charging circuit tests dictate 5.0 volts or greater at 2,500 rpm with the lights running.
Customer Reviews
Read what our customers say about this Yamaha Motorcycle manual and share your own experience.