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Problem and possible cause Remedy
Poor output
1. Insufficient compression 1) Loosen spark plug Retighten; replace gasket
2) Leakage from cylinder head gasket Retighten; replace gasket
3) Piston ring seizure or wear Replace
4) Piston or cylinder wear Repair or replace
5) Incorrect valve and seat contact Repair or replace
6) Valve stem seizure Repair or replace
7) Improper valve clearance Adjust
2. Ignition system problems 1) Faulty spark plug Replace
2) Faulty ignition coil Replace
3) Improper air gap between ignition coil and flywheel Adjust
4) Demagnetization (flywheel magneto) Replace
5) Bad EFI wire harness Replace
3. Fuel system malfunction 1) Throttle body clogged Inspect, replace
2) Fuel strainer and/or hose clogged Clean or replace
3) Air in fuel lines Check and retighten joints
4) Leaky fuel pump pulse line Replace
5) Poor quality gasoline or water in gasoline Replace
6) Bad EFI wire harness Replace
4. Low air intake volume 1) Air cleaner clogged Clean or replace
2) Throttle valve malfunction Repair or replace
Overheat
1. Engine 1) Cooling air flow obstructed at inlet or cylinder baffle
portion
Clean
2) Poor quality engine oil Replace
3) Lean fuel/air mixture Check and adjust carburetor
4) Excessive back pressure of exhaust system Check and clean or replace
5) Overloading Adjust to rated load
Rough Idling
1. Trottle body 1) Low idling speed Adjust
2. Intake system 1) Air mixing from air intake system joints Check and tighten;
replace gasket
3. Cylinder head 1) Gasket faulty (blow-by) Replace
4. Valve system 1) Improper valve clearance Adjust
2) Leakage from valve seat Repair
3) Excessive clearance between valve stem and guide Replace
5. Ignition system 1) Weak spark Check; adjust or replace
plug