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25CC 2-CYCLE ENGINE
Internal Engine Disassembly Inspection & Repair
Engine Start Requirements and Inspection
■ Ignition System: Require a strong spark in the best ignition time. Inspection sequence (from exit to
entrance): spark plug → spark plug cap → starter switch → high voltage line, ground line and on-off
switch line → igniter→ rotor.
■ Fuel System and Carburetor: Air and fuel mixture supplied at the optimum ratio. Inspection
sequence (from entrance to exit): fuel tank cap → fuel → fuel lter → fuel tube → carburetor →
carburetor intake.
■ Compression: Keep optimum cylinder pressure. No loss in this pressure. Inspection sequence (from
external to internal): external condition → fastening condition → cylinder → piston → crankcase.
■ Battery: Sufcient battery capacity.
■ Electric motor: Good motor performance.
Engine Disassembly and Inspection
■ Spark plug: Inspect the spark status. Remove carbon deposit. Inspect electrodes for wear and
deposits. Adjust the spark plug gap (0.65±0.05mm).
■ Air lter: Clean the air lter after every 5 hours of use. Inspect the lter for damage and replace with
a new lter if necessary.
■ Carburetor: Adjust the L/H/T screws when adjusting the carburetor.
■ Remove the rear engine cover, connection cover, clutch and front engine cover.
■ Clutch: If the engine speed is lower than 4200 RPM and the trimmer head rotates rapidly, the clutch
needs to be replaced.
■ Electric starter assembly: If the electric starter malfunctions, disassemble it to check if the electric
motor is broken; test if the wires are in good condition and the gears are in working order.
■ Fuel tank: Check if there is leakage in the tank or in the fuel tube connection. Replace the fuel tank
if leakage occurs.
■ Mufer: Check and clean carbon deposit. The trimmer should never be operated without the mufer
in place.
■ Flywheel (rotor): If the engine overheats, check if rotor ns are in good condition. Always replace
the rotor if rotor ns are missing or if there is visible damage to the rotor. If the spark is too small,
check the magnets. Test the rotor magnets by placing a large socket on the rotor magnets. Shake
the rotor, the magnets should hold on to the socket unless the eld is weak.
■ Ignition coil: Check if the high voltage power line is in good condition. Ensure the rotor air gap is
0.012-0.015 in. (0.30-0.40 mm).
■ Crankcase: Pressure and vacuum test the crankcase.
■ Cylinder: If the above issues are checked and xed and the engine still malfunctions, examine the
cylinder exhaust, piston, and piston ring for carbon buildup. If the exhaust port is clogged, rotate the
piston until it fully covers the exhaust port, and then carefully remove the carbon with a plastic or
wooden scraper. Do not scratch the piston or damage the edges of the exhaust port.
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