If the valve is open, replace the thermostat with a new one.

The thermostat must be completely submerged and must not touch the container sides or bottom. Suspend an accurate thermometer [B] in the water so that the heat sensitive portions [C] are located in almost the same depth.
It must not touch the container, either.
If the measurement is out of the specified range, replace the thermostat with a new one.
Thermostat Valve Opening Temperature
58
62°C (136
144°F)

Thermostat Installation
Hoses and PipesCheck 3-7 Stop Watch Inspection
Connect the leads in the same circuit as Check 3-2.
By pushing the upper button each time to set the stop
watch mode.
Connect the insulated auxiliary lead processed insulation
to the terminal [13] as shown in the figure, then stop watch
start to count.
While count the stop watch, conn ...
Air Intake Duct Assembly (Other than US, CA and CAL Models)
Install the seals [A] as shown in the figure.
Fit the projections [A] of the air intake valve to the hole [B]
of the air intake ducts.
Tighten:
Torque - Air Intake Duct Assembly Screws: 1.5 N·m (0.15
kgf·m, 13 in·lb)
Hang the shaft [A] to the air intake valve securely ...
Idle Speed Inspection
Start the engine and warm it up thoroughly.
With the engine idling, turn the handlebar to both sides
[A].
If handlebar movement changes the idle speed, the
throttle cables may be improperly adjusted or incorrectly
routed, or damaged. Be sure to correct any of these
conditions before rid ...