Yamaha EF1000iS Service Manual page 90

ENGINE SPEED IS UNEVEN
Check fuel level.
SUFFICIENT
Check if fuel is deteriorated.
GOOD
Check if fuel tank cap is clogged.
GOOD
Check if fuel cock is clogged.
GOOD
Check fuel pump operation.
GOOD
Check spark plug for dirt and check spark plug gap.
GOOD
Check valve clearance.
GOOD
While the engine is operating, pull the choke knob
approximately 1/3 to 1/2 way out, and then check the
engine operating condition.
STABLE
Check for air suction due to a damaged throttle shaft
seal, carburetor joint, or gasket.
GOOD
Check if slow or main passages such as, the pilot jet
and main jet, in carburetor are clogged.
GOOD
Check valve face and valve seat for wear.
GOOD
Check if there is seizure or wear on piston, piston ring,
or cylinder.
GOOD
Check the condition of the throttle control system.
Refer to "THROTTLE CONTROL SYSTEM".
INSUFFICIENT
NO GOOD
NO GOOD
NO GOOD
NO GOOD
NO GOOD
OUT OF SPECIFICATION
UNSTABLE
NO GOOD
NO GOOD
NO GOOD
SEIZURE OR
WEAR
6-5
TRBL
ENGINE
Add.
Replace fuel.
Replace.
Clean.
Replace.
Clean, adjust or replace.
Adjust.
Resurface or replace.
Disassemble or replace.
Disassemble or clean.
Resurface or replace.
Rebore or replace.