The seat must be removed and the rear of the tank elevated to gain access to the vacuum connections and synchronizing screw.
The valve clearances must be set properly before synchronizing the carburetors.
The carburetors are numbered 1, 2, 3, and 4 from the left when viewed from astride the motorcycle.
1. Remove the vacuum pipe from the carburetor manifold (No. 3 cylinder) and turn the fuel cock to "PRI."
2. Remove the rubber caps from the No. 1, 2, and 4 carburetor manifolds.
1. Rubber cap
3. Remove either the left or right (but not both) blind plug at the end of the YICS (Yamaha Induction Control System) passage in the cylinder.
1 Blind plug
4. Insert the YICS shut-off tool (special tool) fully and flip the locking lever.
5. Connect each vacuum gauge hose to its proper carburetor.
1. Vacuum gauge
6. Start the engine and allow it to warm up for a few minutes. The warm-up is complete when the engine responds normally to the throttle opening.
7. Make sure the engine idle speed is 950 ~- 1,000 r/min. If it is not adjust the idle speed with the throttle stop screw.
With the YICS shut off tool fitted, the engine speed generally drops a little. Thus, continue with the following steps at an idle speed of 950 — 1,000 r/min.
8. Each gauge reading will indicate the same if the carburetors are synchronized. The No. 3 carburetor has no synchronizing screw, and the other carburetors are to be synchronized to it in order, one at a time. First, synchronize carburetor No. 1 to carburetor No. 2 by turning the No. 1 synchronizing screw until both gauges read the same.
Second, in the same way synchronize carburetor No. 4 to carburetor No. 3. Third, by adjusting No. 2 screw, watch No. 3 carburetor reading. No. 1 and No. 2 carburetors will both change to match No. 3 carburetor.
9. Remove the YICS shut-off tool and reinstall the blind plug.
22 Nm (2.2 mkg, 16 ft-lb)
10. Check the idle speed. Adjust if necessary.
Idle speed adjustment
Carburetors must be synchronized before setting the final idle speed. The idle speed adjustment is made by turning only one throttle stop screw.
1. The engine must be warmed up, before setting the idle speed.
2. Set the engine idle speed by turning the throttle stop screw in (to increase engine speed) or out (to decrease engine speed).
Standard idle speed: 1,100 r/min
1. Throttle stop screw