TROUBLESHOOTING
35
2
FOUR-STROKE ENGINE OPERATING PRINCIPLES
Intake valve opens
as piston begins
downward, drawing
air/fuel mixture into
the cylinder through
the valve.
COMPRESSION
INTAKE
Intake valve
closes and
piston rises
in cylinder,
compressing
air/fuel
mixture.
EXHAUST
POWER
Spark plug
ignites
compressed
mixture,
driving piston
downward.
Force is applied
to crankshaft,
causing it to
rotate.
1
Air/fuel
Cylinder
Intake valve
Carburetor
Exhaust
valve
Exhaust
Exhaust valve
opens as piston
rises in cylinder,
pushing spent
gasses out through
the valve.