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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
adjusting needles out (counterclockwise) increases
the supply of fuel to the carburetor.
Idle Speed Screw
Figure 9.
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 light/y.
2. Preliminary Settings: Turn the adjusting
needle(s) out (counterclockwise) from lightly
bottomed as follows or to the rich side of
adjustment.
K241
K301
K321
K341
Walbro Fixed Jet
Low Idle
l-l I4 turns
1-l /4 turns
l-l I2 turns
1 turn
Walbro Adjustable Jet
I
Low Idle
Main Idle
K241
K301
K321
K341
I-314 turns
I-314 turns
I-l /a turns
2-112 turns
l-l 18 turns
l-l I8 turns
l-l I4 turns
l-l 14 turns
3. Start the engine and run at half throttle for five to
ten minutes to warm up. The engine must be
warm before making final settings.
4. Main Fuel Needle Setting: This adjusfment is
required only for adjustable main jet carburetors.
If the carburetor is a fixed main jet type, disregard
this setting.
Place the throttle into the “fast” position.
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. Back the needle out approximately
l/4 turn. See Figure 10 for best main fuel
performance.
Back out
Appx. 118
to II4
Lean
turn.
Lean
CI
I
\
\
I
I
\I
@
Figure 10. Optimum Main Fuel Setting.
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 the equipment
manufacturer’s instructions for specific
low idle speed settings. To ensure best
results when setting the low idle fuel
needle, the low idle speed must not
exceed 1500 RPM.
12