Evinrude 4906B 4HP 1969, Owner'S Manual

Page: 33 / 422

2-8 TUNING
filters, lines, and passageway in the carbu-
retor.
If the condition of the fuel is in doubt,
drain, clean, and fill the tank with fresh
fuel.
Fuel pressure at the carburetor should be
checked whenever a lack of fuel volume at
the carburetor is suspected.
High-speed Adjustment
The high-speed needle valve is adjustable
on most models covered in this manual
through 1965. After 1965, the high-speed
needle valve is fixed at the factory and is
NOT adjustable. However, larger or smaller
needle valves may be installed for different
elevations. On all Johnson/Evinrude en-
gines, the high-speed needle valve is the
lower valve on the carburetor. The upper
needle is always the idle adjustment.
A beginning "rough" adjustment for the
high-speed needle valve is 3/'+ turn out
(counterclockwise) from the lightly seated
(closed) position. TAKE CARE not to seat
the valve firmly to prevent damage to the
valve or the carburetor.
To make the high-speed adjustment:
a- Mount the engine in a test tank or
body of water, preferably with a test wheel.
Engines up to '+0 hp may be operated in the
high rpm range in a test tank without sus-
taining damage.
NEVER, AGAIN NEVER, operate the en-
gine at high speed with a flush device at-
tached. The engine, operating at high speed
with such a device attached, would RUN-A-
WAY from lack of a load on the propeller,
causing extensive damage.
D- Connect a tachometer to the engine.
A
35
hp unit showing location
of
the idle
and
high-
speed adjustments. Notice the pressure-type fuel con-
nector.
CAUTION: Water must circulate through
the lower unit to the engine any time the en-
gine is run to prevent
damage to the water
pump in the lower unit. Just five seconds
without water will damage the water pump.
c-
Start the engine and allow it to warm
to operating temperature.
d- Shift the engine into forward gear.
e- With the engine running in forward
gear, advance the throttle to the wide open
position, and then very SLOWLY turn the
high-speed needle valve inward (CLOCK-
WISE) until the engine begins to loose rpm.
Now, SLOWLY rotate the needle valve out-
ward (COUNTERCLOCKWISE) until the en-
gine peaks out at the highest rpm.
If the high-speed needle valve adjust-
ment is too lean, the low-speed adjustment
will be affected. Under certain conditions
it may be necessary to adjust the high-speed
needle valve just a bit richer in order to
obtain a satisfactory idle adjustment.
After the high-speed needle adjustment
has been obtained, proceed with the idle ad-
justment as outlined in the next paragraphs.
Idle Adjustment
Due to local conditions, it may be neces-
sary to adjust the carburetor while the en-
gine is running in a test tank or with the
boat in a body of water. For maximum
performance, the idle mixture and the idle
rpm should be adjusted under actual operat-
ing conditions.
Set the idle mixture screw at the speci-
fied number of turns open from a lightly
seated position. In most cases this is from I
to 1 Y2 turns open from close.
Small horsepower engine mounted
in a
test tank
with the low- and high-speed adjustments indicated.