1974 Yamaha DT250A / DT360A Service Manual (207 Pages)

Enhanced Repair Manual: Yamaha DT250A / DT360A 1974 Service Manual Specification-Guide

Model-Portfolio: Yamaha DT250A, DT360A — 1974 models // Model-Designation: Twin-stroke motorcycle engine systems, fuel delivery, and electrical circuits // Model-Designation: Comprehensive mechanical specifications, torque documentation, and assembly procedures.

Reference chapters include engine assembly and disassembly procedures, carburetion and fuel system design, electrical systems and wiring schematics, chassis suspension and brake components, and transmission shift mechanism operation, covering the complete mechanical and electrical architecture of both DT models.

Diagnostic procedures are covered for ignition timing, carburetor circuit troubleshooting, and electrical component function verification. Wiring diagrams are provided for DT250A magneto and DT360A capacitor discharge ignition configurations. Fuel system procedures are documented for petcock operation, float level adjustment, and reed valve assembly maintenance. Adjustment procedures are detailed for throttle cable synchronization, clutch engagement geometry, and brake lever freeplay. Timing procedures are documented for piston position determination and spark occurrence validation.

The manual documents torque specifications for the cylinder head fasteners to ensure proper component alignment retention. Yamaha designed these machines with emphasis on both trail-riding versatility and road performance capability. The integrated Autolube pump delivers oil directly to the intake port, eliminating the need for fuel-oil premixing. Engine disassembly requires understanding the crankcase split method and proper bearing removal procedures. Transmission shafts require precise end-play measurement before final reassembly. The two-stroke design incorporates a forward-inclined cylinder with torque induction porting, complemented by a reed valve inlet system that operates independently based on crankcase pressure dynamics.

Specifications detail the DT250A displacement at 246cc with 70×64mm bore and stroke, while the DT360A reaches 351cc with 80×70mm dimensions. Both models utilize a primary gear reduction ratio controlling drive from the crankshaft to the clutch housing. Chassis specifications include 55.7-inch (DT250A) and 56.1-inch (DT360A) wheelbase measurements, with front telescopic forks and rear swinging arm suspension. Wheel and tire systems incorporate internal expansion brake drums on both axles. The electrical system provides 6-volt charging through a dual-output magneto coil with silicon rectifier, supplying power to the 4AH battery for horn, stoplight, and signal circuits while maintaining separate alternating current paths for headlight and taillights.