Engine Overheat; Abnormal Sound - Yamaha MA190 Service Manual

4-1-5 Engine overheat

TROUBLE
Oil insufficient or wrong oil ratio in the gaso-
line
Exhaust pipe blocked up.
Shroud leaking
Cooling fins blocked by foreign matter.
Cooling fan is loosen and malfunction.
Gasoline
Connection rod deformation to make piston
engine
and cylinder bushing side wear
overheat
Cylinder or piston or piston ring is worn to
make hunting between cylinder and crank-
case.
Improper adjustment of engine governor to
produce speed high
Crankshaft main bearing burnt out.

4-1-6 Abnormal sound

TROUBLE
Piston, piston ring or cylinder is worn.
Connection rod or piston pin and piston pin
hole are worn.
Beating sound
Crankshaft main neck is worn.
Piston ring is broken.
Too much carbon deposit in combusting
chamber
Metal beating
sound when
Too small electrode clearance of spark plug
abnormal com-
bustion occurs
Engine fuel is too much.
Improper fuel brand
Engine is overheat.
The other
Improper valve clearance
Fly wheel is not connected with crankshaft
tightly.
CAUSE
CAUSE
24
4-1 Troubleshooting
REMEDY
Refill engine oil.
Clean exhaust pipe.
Repair damaged part.
Clear cooling fins.
Reinstall well.
Replace connection rod.
Replace the worn parts.
Readjust engine governor.
Replace main bearing.
REMEDY
Replace the worn part.
Replace the worn part.
Replace bearing.
Replace piston ring.
Clear away carbon deposit.
Adjust electrode clearance
properly.
Check relative parts such as
carburetor.
Replace fuel.
Find a cause and eliminate it.
Readjust valve clearance prop-
erly.
Connect tightly.