Carburetor

NOTE:
The carburetors are numbered 1, 2, 3, and 4 from the left when viewed from astride the motorcycle.

1.    Idle mixture

The idle mixture is set at the factory by the use of special equipment. No attempt should be made by the dealer to change this adjustment.

2.    Synchronization

The seat must be opened and the rear of the tank elevated to gain access to the vacuum connections and synchronizing screw of the carburetors.

NOTE:
The valve clearances must be set properly before synchronizing the carburetors.

a.   Remove the vacuum pipe from the carburetor manifold (No. 2 cylinder) and turn the fuel petcock to "PRI".

b.   Remove the rubber caps from the No. 1, 3, and 4 carburetor manifolds.

1, Vacuum pipe 2. Rubber cap

c.   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.

d.   Insert the YICS shutoff tool (special tool) fully and flip the locking lever.

e.   Connect each vacuum gauge hose to its proper carburetor.

1. Vacuum gauge

f.   Start the engine allow it to warm-up for a few minutes. The warm-up is complete when engine responds normally to the throttle opening.

g.   Make sure the engine idle speed is 1,000 ~~ 1,100 r/min. If it does not, adjust the idle speed with the throttle stop screw.

NOTE:
With the YICS shutoff tool fitted, the engine speed generally drops a little. Thus, continue with the following steps at idle speed of 1,000~ 1,100 r/min.

h. 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 to watch No. 3 carburetor reading, No. 1 and No.2 carburetors will both change to match No. 3 carburetor.

1. Synchronizing screws

i. Make sure that the engine now develops an idle engine speed of 1,000 ~ 1,100 r/min. If it does not, adjust the idle speed with the throttle stop screw and repeat the steps starting with g.

j. Remove the YICS shutoff tool and reinstall the blind plug.

Tightening torque:

2.2m-kg (16.0ft-lb)

3. Idle speed adjustment

NOTE:
Carburetors must be synchronized before setting final idle speed. The idle speed adjustment is made by turning only one throttle stop screw.

a.   The engine must be warmed up before setting idle speed.

b.  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: 1,200 r/min

1. Throltle stop screw