Evinrude 4906B 4HP 1969 Owner's Manual page 48

or other wind instrument.
is closed and seals the opening to which it is
attached. the case of an outboard engine,
In
this opening is between the crankcase
the carburetor. The reeds are mounted in
the intake manifold, just behind the carbu-
retor.
Actual
Operation
The piston creates
as it moves up and down in the cylinder.
the piston moves upward, a vacuum is creat-
ed in the crankcase
On the compression stroke, when the piston
moves downward, the reed is forced closed.
Reed Designs
A wide range of reeds, reed plates, and
reed box installations
outboard unit, due to the varying, designs of
the engines. All installations
same principle and there is no difference
their operation.
Broken Reed
A broken reed is usually caused by metal
fatigue over a long period of time.
failure may also be due to the reed flexing
too far because the reed stop has not been
adjusted properly or the stop has become
distorted. If the reed is broken, the loose
piece MUST be located and removed, before
the engine is returned to service.
of reed may have found its way into the
crankcase, behind the bypass cover.
2 CYCLE
INTAKE PORT
ABOUT TO
OPEN
FUEL IN
CRANKCASE
EXHAUST
to
Diagram illustrate
board engine.
At rest, the reed
vacuum and pressure
pulling the reed open.
may be found on an
employ the
The
The piece
If the
PRESSURE
IN CRANKCASE
REED VALVE
CLOSED
of a two-cycle
operation
and
BROKEN
As
REED
VALVE
Cross-section
reed in the crankcase.
broken piece cannot be located, the power-
in head must be completely
it is located and removed.
The accompanying
how a broken reed will cause a backflow
through the carburetor.
An excellent
an operating
business card in front
Under normal operating
small amount of fine mist will be notice-
able, but if fuel begins to appear rapidly on
the card from the carburetor,
reeds is broken and causing the back flow
through the carburetor
A broken reed will cause the engine to
operate roughly
through the carburetor.
out-
REED SERVICE
of a
cylinder to illustrate
disassembled
illustration
check for a broken reed on
engine is to hold an ordinary
of the carburetor.
conditions,
and onto the card.
and with a "pop" back
a
Reed box with broken reed.
3-7
a
broken
until
depicts
a very
one of the