The 1975-1979 Yamaha RD400 Twins repair manual by Haynes covers the following RD models:
Book Excerpt: 1975-1979 Yamaha RD400 Twin Repair and Service Manual
- Yamaha RD400 398cc, U.S.A. 1975, U.K. 1976
- Yamaha RD400E 398cc, U.K. 1978
FUEL SYSTEM AND LUBRICATION
SYNCHRONIZING TWIN CARBURETORS
WHEELS, BRAKES AND TIRES
- For optimum performance and even running, it is important that both carburetors are in phase, so that they open and close together and have the same settings throughout the entire throttle range.
If this type of check is not carried out at regular intervals, one cylinder may do all the work, while 'carrying' the other.
The usual symptoms of poor balance between the two carburetors are difficulty in starting and uneven running at low speeds, accompanied by a noticeable lag when accelerating.
- To check whether the carburetors are correctly synchronized, remove the aligning orifice plug from the right-hand side of each carburetor and open the throttle fully.
By viewing through the aperatures, check that the lower edge of the aligning marks on the throttle valves align exactly with the lower edge of each aperature.
- If alignment is incorrect adjust each carburetor independently by means of the cable adjuster in each carburetor top. Finally, replace the orifice plugs.
- Remove the plug cap from the left-hand spark plug and start the engine. Screw in (clockwise) the throttle stop screw of the right-hand carburetor until the engine will continue to run on one cylinder at a reasonably low speed.
Check whether adjustment of the pilot screw from the recommended setting of one and a half complete turns out has any noticeable effect on even running and readjust the throttle stop screw as necessary. Stop the engine.
- Repeat the above operation with the right-hand spark plug cap removed and adjust the left-hand carburetor. Stop the engine when the adjustment seems correct. Each cylinder should run independently at the same speed.
- Re-start the engine with both plug caps connected. Most probably the tick-over will now be too fast, in which case the throttle stop screws of each carburetor can now be screwed out an equal amount (a little at a time) until the desired engine speed is attained.
Normally this is in the region of 1300 to 1400 rpm, as indicated by the tachometer.
BLEEDING THE HYDRAULIC SYSTEM
- As mentioned earlier, brake action is impaired or even rendered inoperative if air is introduced into the hydraulic system. This can occur if the seals leak, the reservoir is allowed to run dry or if the system is drained prior to the dismantling of any component part of the system.
Even when the system is refilled with hydraulic fluid, air pockets will remain and because air will compress, the hydraulic action is lost.
- Check the fluid content of the reservoir and fill almost to the top. Remember that hydraulic brake fluid is an excellent paint stripper, so beware of spillage, especially near the gas tank.
- Place a clean glass jar below the brake caliper unit and attach a clear plastic tube from the caliper bleed screw to the container. Place some clean hydraulic fluid in the container so that the pipe is always immersed below the surface of the fluid.
- Unscrew the bleed screw one complete turn and pump the handlebar lever slowly. As the fluid is ejected from the bleed screw the level in the reservoir will fall. Take care that the level does not drop too low while the operation continues, otherwise air will re-enter the system, necessitating a fresh start.
Subject: Transportation: Motorcycles: Yamaha 1975, 1976, 1977, 1978, 1979 RD400 Twin service, maintenance, tuneup and repair. ISBN-10: 0856965480 | ISBN-13: 9780856965487 | Haynes 333