KYMCO Zing 125 Service Manual page 21

1
. GENERAL INFORMATION
POOR PERFORMANCE (ENGINE LACKS POWER)
Inspection/Adjustment
Start engine and accelerate
lightly for observation
Check ignition timing using
a timing light
Check valve clearance
Test cylinder compression
Check carburetor for
clogging
Remove spark plug and
inspect
Check crankcase for oil
level and condition
Remove cylinder head oil
pipe bolt and inspect
Check for engine overheating
Rapidly accelerate or run at
high speed
1-19
Symptom
Engine speed
increases
Correct
Correct
Normal
compression
Not clogged
Plug not fouled or
discolored
Correct and not
contaminated
Valve train lubricated
properly
Engine does not
overheats
Engine does not knock
Engine speed does not
increase sufficiently
Incorrect
Incorrect
Abnormal
compression
Clogged
Plug fouled or
discolored
Incorrect or
contaminated
Valve train not
lubricated properly
Engine overheats
Engine knocks
Probable Cause
Clogged air cleaner
Poor fuel flow (Restricted)
Clogged fuel tank cap breather hole
Clogged exhaust muffler
Carburetor fuel level too low
Clogged carburetor high speed fuel
passage
Faulty CDI unit
Faulty pulser coil
Improper valve clearance
adjustment
Excessively worn valve seat
(protruded valve stem)
Improper valve and seat contact
Worn cylinder and piston rings
Leaking cylinder head gasket
Improper valve timing
Clean and unclog
Fouled spark plug
Incorrect heat range plug
Oil level too high
Oil level too low
Oil not changed
Clogged oil cooler
Clogged oil line
Faulty oil pump
Worn cylinder and piston rings
Mixture too lean
Poor quality fuel
Excessive carbon buildup in
combustion chamber
Ignition timing too advanced
Excessive carbon build-up in
combustion chamber
Poor quality fuel
Clutch slipping
Mixture too lean
Ignition timing too advanced