1977 Yamaha YZ80 Service and Repair Manual

Coded YZ80D, the 1977 YZ80 has its own factory manual, LIT-11626-00-42, written for that model year and no other.

The engine chapters set out piston and bore dimensions, clutch and gearbox procedures and the order in which the cases come apart, alongside the carburetor settings and ignition timing Yamaha specified new. Chassis material covers fork and shock service, wheel and brake work, bearing replacement and the frame torque figures.

Working on a bike of this age, the useful thing about original literature is that it tells you what standard looks like. Anything on your machine that differs from these diagrams is a modification, not a fault, and knowing which is which saves a great deal of time. Check the frame for YZ80D, then work from LIT-11626-00-42.