The 1970-1979 Yamaha RD250, RD350, YDS7, YR5 Twins repair manual by Haynes, covers the following models:

• Yamaha YDS7, 1970-1973 U.K.
• Yamaha RD250, 1973-1975 U.K., U.S.A.
• Yamaha RD250DX, 1976-1979 U.K.
• Yamaha YR5, 1970-1973 U.K.
• Yamaha RD350, 1973-1975 U.K., U.S.A.
• Yamaha RD350B, 1975-1976 U.K.

Book Excerpt: 1970-1979 Yamaha RD250, RD350, YDS7, YR5 Repair Manual CHAPTER 1 | ENGINE, CLUTCH AND TRANSMISSION

STARTING AND RUNNING THE REBUILT ENGINE

1. When initial start-up is made, run the engine slowly for the first few minutes, especially if the engine has been rebored or a new crankshaft fitted. Check that all the controls function correctly and that there are no oil leaks before taking the machine on the road. The exhaust will emit a high proportion of white smoke during the first few miles, as the excess oil used while the engine was reassembled is burnt away. The volume of smoke should gradually diminish until only the customary light blue haze is observed during normal running. It is wise to carry a spare pair of spark plug wires during the first run, since the existing plugs may oil up due to the temporary excess of oil.
2. Remember that a good seal between the pistons and the cylinder barrels is essential for the correct functioning of the engine. A rebored two-stroke engine will require more carefully running-in over a longer period, than it's four-stroke counterpart. There is a far greater risk of engine seizure during the first hundred miles if the engine is permitted to work hard.
3. Do not tamper with the exhaust system or run the engine without the baffles fitted to the silencer. Unwarranted changes to the exhaust system will have a very marked effect on engine performance, invariably for the worst. The same advice to dispensing with the air cleaner or the air cleaner element.
4. Do not on any account add oil to the gas under the mistaken belief that a little extra oil will improve the engine lubrication. Apart from creating excess smoke, the addition of oil will make the mixture much weaker, with the consequent risk of overheating and engine seizure. The oil pump alone should provide full engine lubrication.

CHAPTER 4 | FRAME AND FORKS

STEERING HEAD LOCK

1. The steering head lock is attached to the left-hand side of the steering head. It is retained by a rivet. When in a locked in position, the plunger extends and engages with a portion of the steering head stern, so that the handlebars are locked in position and cannot be turned.
2. If the lock malfunctions, it must be renewed. A repair is impractical. When the lock is changed it follows that the key must be changed too, to correspond with the new lock.

STEERING DAMPER | FUNCTION AND USE

1. A steering damper is a fitting providing a means of adding friction to the steering wheel assembly so that the forks will turn less easily. It is a relic of the early days of motorcycling when machines were prone to develop "speed wobbles" which grew in intensity and eventually unseated the rider. With today's more sophisticated front form damping and improved frame design, a steering damper is virtually a superfluous fitting unless a sidecar is attached or very poor road surfaces are encountered.
2. The steering damper can be likened to a small clutch without the compression springs. when the steering damper knob is tightened, the friction discs and the plain discs of the assembly are brought into closer proximity and it is more difficult to deflect the handlebars from their set position. When the knob is tightened fully, the handlebars are locked in position. Under normal road conditions, the steering damper should be slacked off. Only at very high speeds or on rough surfaces is there any need to apply some damper friction.
3. The steering damper assembly will be found at the base of the steering head column, immediately below the bottom fork yoke. The center fixed plate is attached to the fork yoke by a bolt and washer.
4. Although it is unlikely that the steering damper assembly will require attention during the normal service life of the machine, it can be removed by releasing the split pin through the extreme end of the rod attached to the steering damper rod, as described in Section 2.4 of this Chapter. The remainder of the assembly is freed when the bolt retaining the center plate in position is withdrawn from the underside of the bottom fork yoke.

Subject: 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979 Yamaha RD250, RD350, YDS7, YR5 service, maintenance, repair. ISBN-10: 0856965057 | ISBN-13: 9780856965050 | Haynes 040