12
Set the adjusting needle
midway
between the rich
and lean settings.
Figure 9.
7. Recheck the idle speed using a tachometer.
Readjust the speed as necessary.
Walbro Carburetor Adjustment
In general, turning the adjusting needles
in
(clockwise)
decreases the supply of fuel to the carburetor. This
gives a
leaner
fuel-to-air mixture. Turning the
adjustment needles
out
(counterclockwise) increases
the supply of fuel to the carburetor.
Figure 10.
NOTE: The tip of the low idle fuel and main fuel
adjusting needles are tapered to critical
dimensions. Damage to the needles and the
seats in carburetor body will result if the
needles are forced.
1. With the engine stopped, turn the adjusting
needle(s)
in
(clockwise) until it bottoms
lightly
.
2.
Preliminary Settings:
Turn the adjusting
needle(s)
out
(counterclockwise) from lightly
bottomed as shown in the chart or page 13, or to
the rich side of adjustment.
Adjust To
Midpoint
Lean
Rich
Idle Speed Screw
Low Idle
Fuel Needle
Main Fuel Needle
3. Start the engine and run at half throttle for 5 to 10
minutes to warm up. The engine must be warm
before making final settings (steps 4, 5, 6, and 7).
4.
Main Fuel Needle Setting:
This adjustment is
required for adjustable main jet carburetors only. If
the carburetor is a fixed main jet type, refer to
Walbro adjustment.
Place the throttle into the ‘‘fast’’ position. If
possible, place the engine underload.
Turn the main fuel adjusting needle
out
(counterclockwise) from the preliminary setting
until the engine speed decreases (rich). Note the
position of the needle.
Now turn the adjusting needle
in
(clockwise). The
engine speed may increase, then it will decrease
as the needle is turned in (lean). Note the position
of the needle.
Set the adjusting needle
midway
between the rich
and lean settings.
5.
Low Idle Speed Setting:
Place the throttle control
into the
“idle”
or
“slow”
position. Set the low idle
speed to
1200 RPM*
(± 75 RPM) by turning the
low idle speed adjusting screw
in or out
. Check
the speed using a tachometer.
*NOTE: The actual low idle speed depends on the
application – refer to equipment
manufacturers recommendations. The
recommended low idle speed for basic
engines is 1200 RPM. To ensure best
results when setting the low idle fuel
needle, the low idle speed must not
exceed 1500 RPM.
6.
Low Idle Fuel Needle Setting:
Place the throttle
into the
“idle”
or
“slow”
position.
Turn the low idle fuel adjusting needle
out
(counterclockwise) from the preliminary setting
until the engine speed decreases (rich). Note the
position of the needle.
Now turn the adjusting needle
in
(clockwise). The
engine speed may increase, then it will decrease
as the needle is turned in (lean). Note the position
of the needle.
