Yamaha EF2000iS Manuel D'atelier page 238

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 spark plug for dirt and check spark plug gap.
GOOD
Check valve clearance.
GOOD
Check the choke function. (*1)
GOOD
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
NOT GOOD
NOT GOOD
NOT GOOD
NOT GOOD
OUT OF SPECIFICATION
NOT GOOD
NOT GOOD
NOT GOOD
NOT GOOD
SEIZURE OR
WEAR
ENGINE
Add.
Replace fuel.
Replace.
Clean.
Clean, adjust or replace.
Adjust.
Clean or replace.
Disassemble or replace.
Disassemble or clean.
Resurface or replace.
Rebore or replace.
(*1): If the engine speed becomes stable by pulling
the choke knob by 1/3 or 1/2 while the engine speed
is unstable, this indicates there is clogging in the main
passages.
6-5
TRBL