When the engine is running, the air intake valve is lifting up.
If the valve does not operate properly, check the air intake solenoid valve hoses for leak.
If there are no leaks, check the air intake solenoid valve.

Air Intake Solenoid Valve Unit TestCooling System Flushing
Over a period of time, the cooling system accumulates
rust, scale, and lime in the water jacket and radiator. When
this accumulation is suspected or observed, flush the cooling
system. If this accumulation is not removed, it will clog
up the water passage and considerable reduce the efficiency
...
Seat Cover Installation
Installation is the reverse of removal. Note the following.
When installing the pad [A], install it along the corner [B]
as shown in the figure.
When installing the pad [C], align the ends [D], along the
corner [E], and wrap [F] the upper edge of the seat cover.
Install the damper [A] ...
Shift Drum Assembly
Press and insert the ball bearing [A] on the shift drum [B]
until it is bottomed.
Install:
Ball Bearing [C]
Dowel Pin [D] and Shift Drum Cam [E]
Align the pin with the groove in the shift drum cam.
Apply a non-permanent locking agent to the shift drum
cam holder bolt [F].
Tight ...