Synchronizing The Carburetors
WARNING! Please be aware that the Yamaha Service Manual has the procedure for syncing the carburetors WRONG. The manual indicates that screw 1 is used to sync carb 1 to carb 2 and that screw 3 is used to sync carb 3 to carb 2. That is opposite of what it should be. The following is the correct procedure.
NOTE: Prior to synchronizing the carburetors, the valve clearance and the engine idling speed should be properly adjusted and the ignition timing should be checked.
1. Stand the motorcycle on a level surface.
NOTE: Place the motorcycle on a suitable stand.
2. Remove vacuum plugs.
3. Install: Adapters Vacuum gauge (Fig.2) Engine tachometer (Fig.2) to the spark plug lead of cyl. #1.
Vacuum gauge: YU-08030-A, 90890-03094 (These are Yamaha part numbers. Any suitable mercury sticks, or other suitable gauges are just fine)
Engine tachometer: YU-08036-A, 90890-03113 (Yamaha part numbers. Any suitable tachometer will work. A tachometer is not absolutely required
4. Start the engine and let it warm up for several minutes.
5. Check engine idling speed. If out of specification, adjust to 950 to 1050 RPM.
Refer to "ADJUSTING THE ENGINE IDLING SPEED". in your service manual
6. Adjust carburetor synchronization.
A. (Fig.3) Synchronize carburetor #1 to carburetor #2 by turning the synchronizing screw (3) in either direction until both gauges read the same.
NOTE: After each step, rev the engine two or three times, each time for less than a second, and check the synchronization again.
B.Synchronize carburetor #4 to carburetor #3 by turning the synchronizing screw (2) in either direction until both gauges read the same.
NOTE: Turning screw clockwise raises carburetor #4 and lowers carburetor #3.
C. Synchronize carburetor #2 to carburetor #3 by turning the synchronizing screw (1) in either direction until both gauges read the same.
NOTE: Turning screw clockwise raises carburetor #3 and lowers carburetor #2.
Vacuum pressure at engine idling speed is 37 kPa (280 mmHg).
NOTE: The difference in vacuum pressure between two carburetors should not exceed 1.33 kPa (10.0 mmHg, 0.4 inHg).
7. Check engine idling speed. If out of specification, adjust.
8. Stop the engine and remove the measuring equipment.
Yamaha then recommends the following.
9. Adjust:
Throttle cable free play Refer to "ADJUSTING THE THROTTLE CABLE FREE PLAY".
Throttle cable free play (at the flange of the throttle, grip) 4 - 6 mm (0.16 - 0.24 in)
10. Install vacuum plugs.
