Evinrude 4906B 4HP 1969 Owner's Manual page 42

3-1 INTRODUCTION
The carburetion
of two-cycle engine operation
derstood in order to perform a proper tune-
up on an outboard
would be well worth the time to study the
principles of two-cycle
in this section.
A Polaroid, or equivalent
camera, is an extremely
ing the means of accurately
arrangement of parts and wire connections
BEFORE the disassembly work begins.
a record is most valuable during the assemb-
ly work.
Tags are handy to identify
they are disconnected
connected to the same terminal from which
they were removed.
used for parts where marks or other
of identification are not possible.
THEORY OF OPERA nON
The two-cycle engine differs in several
ways from a conventional
mobile) engine.
1- The method
mixture is delivered
chamber.
2-
The complete lubrication system.
3- In most cases, the ignition system.
4-
The frequency of the power stroke.
These differences
and compared with four-cycle
tion.
Intake/Exhaust
Two-cycle engines
ment of port openings to admit fuel to the
combustion chamber
haust gases after
pleted. The ports are located
POWERHEAD
and ignition principles
be un-
MUST
motor. Therefore,
engines as outlined
instant-type
useful item provid-
recording
wires after
to ensure they will be
These tags may also be
means
four-cycle (auto-
by which the fuel-air
to the combustion
will be discussed briefly
engine opera-
utilize an arrange-
and to purge the ex-
burning has been com-
in a precise
3
pattern in order for them to be open and
closed off at an exact moment by the piston
as it moves up and down in the cylinder.
The exhaust port is located
than the fuel intake port.
opens the exhaust port first, as the piston
it
starts downward, and therefore,
phase begins a fraction
the intake phase.
Actually,
are spaced
open almost simultaneously.
the
son, the pistons of most two-cycle
have a deflector-type
Such
the piston
effectively.
DEFLECTOR
Drawing
two-cycle engine.
slightly higher
This arrangement
of a second before
the intake and exhaust
so closely together
top. This design of
top serves two purposes
EXHAUST
PORT
to depict
the intake and exhaust cycles
the exhaust
ports
that both
For this rea-
engines
very
EXHAUST
of a