Benelli TNT125 - Excessive Speed Change; Engine Gives an Abnormal Noise; There Is a Click to Give an Alarm for Fault; There Is Knocking Noise at Piston

Excessive speed change:
 Gear lever spring has poor flexibility or is
damaged;
 The spring at shifting link rod claw
 is broken;
Engine gives an abnormal noise:
There is a “click” to give an alarm for fault:
 Engine control unit (ECU) fails
 There is carbon deposition in combustion
chamber;
 Fuel quality is poor or fuel type is not applicable;
 Spark plug is not applicable;

Engine is overheated.
There is knocking noise at piston:
 The clearance between cylinder and piston is too
large;
 Cylinder and piston is worn;
 Link rod is bent;

Piston pin or piston pin hole is worn;
Valve gives a noise:
 The valve clearance is incorrect;
 Valve spring is damaged or the elasticity is poor;
 Camshaft bearing is worn;
 Valve plunger wear
 Other noises:
 The clearance at the small end of connecting rod is
too large;
 The clearance at the big end of connecting rod is
too large;
 The gap between the piston ring and the piston
ring groove is too large
 Piston ring is worn, damaged or stuck;
 Piston ring groove is worn;
 Piston is seized or damaged;
 Cylinder head gasket leaks;
 The exhaust pipe of cylinder head connecting part
leaks;
 Crankshaft oscillation is too large;
 Engine is loosened;
 Crankshaft bearing is worn;
 Main gear is worn or has a gap;
 Camshaft chain tensioner fault;
 Camshaft chain, sprocket or guide plate is worn;
 The suction valve is broken;
 Secondary air valve is broken;
 Magneto rotor is loosened;
 Overheating of muffler causes melting of catalytic
agent (Benelli emission pollution control system).
The drive system makes an unusual noise:
Clutch noise:
 Clutch shock absorber function is weak or
damaged;
 The clearance between clutch housing and friction
plate is too large;

Clutch shell is worn;
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