Evinrude 4906B 4HP 1969 Owner's Manual page 33

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
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
through 1965. After
needle valve is fixed at the factory
NOT adjustable. However, larger or smaller
needle valves may be installed for different
elevations. On all Johnson/Evinrude
gines, the high-speed
lower valve on the carburetor.
needle is always the idle adjustment.
A beginning "rough" adjustment
high-speed needle
(counterclockwise)
(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,
WAY from lack of a load on the propeller,
causing extensive damage.
D- Connect a tachometer
35
A hp unit showing location
speed adjustments. Notice the pressure-type
nector.
should be
in this manual
1965, the high-speed
and is
needle valve is the
The upper
for the
valve is 3/'+ turn
from the lightly seated
would RUN-A-
to the engine.
of
and
the idle
fuel con-
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
position,
high-speed
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.
en- If the high-speed
ment is too lean, the low-speed adjustment
will be affected.
it may be necessary to adjust the high-speed
needle valve just a bit richer in order to
out obtain a satisfactory
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
gine is running in a test tank or with the
boat in a body of water.
performance,
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.
to 1 Y2 turns open from close.
high-
Small horsepower
with the low- and high-speed adjustments
to the wide open
and then very SLOWLY turn the
needle valve inward
needle valve adjust-
Under certain
idle adjustment.
For maximum
the idle mixture and the idle
In most cases this is from I
engine mounted
(CLOCK-
conditions
while the en-
in a
test tank
indicated.