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SECTION 6B
FUEL SYSTEMS
ADJUSTING WALBRO CARBURETORS
In general, tuming the adjusting needles in (clockwise)
decreases the supply of fuel to the carburetor. This
gives a Јеалег fuel-to-air mixture. Tuming the adjust-
ing needles out (counterclockwise) increases the sup-
Ply of fuel to the carburetor.
Main Fuel Needie
Figure 68-3.
Walbro Adjustable Main Jet Carburetor.
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, tum the adjusting
needle(s) In (clockwise) until it bottoms fightiy.
2. Preliminary Settings: Turn the adjusting
needie(s) out (counterclockwise) from lightly bot-
tomed as follows or to the rich side of adjustment.
H WALBRO FIXED JET
LOW IDLE
]
M18
1-1/4 TURNS
M20
1-1/4 TURNS
| WALBRO ADJ
LOW IDLE
MAIN FUEL
M18
1-1/4 TURNS.
| 1-1/4 TURNS
M20
1-1/4 TURNS
1 TURN
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. Maln Fuel Needle Setting: This adjustment is
possible only on adjustable main jet carburetors.
if the carburetor is a fixed main jet type, disregard
this.
Place the throttle into the "fast" position.
Tum the adjusting needle In (clockwise). The en-
gine speed may increase, then it will decrease as
the needle is tumed in (lean). Note the position of
the needle. Back the needle out approximately
1/4tum.
See Figure 6B-4A for best main fuel
performance.
Back out
Appx.
1/8
to 1/4
Lean
turn.
Lean
е
|
Figure 6B-4A.
Optimum Main Fuel Setting.
5. Low Idle Speed Setting: Piace the throttle con-
tro! into the "idle" or "slaw" position. Set the low
idle speed to 1200 RPM* (+ or - 75 RPM) by
tuming 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 man-
ufacturer's instructions for specific low
idle speed settings. To ensure best re-
sults when setting the low idle fuel
needle, the low idle speed must not ex-
ceed 1500 RPM.
6. Low Idle Fue! Needle Setting: Place the throttle
into the "idle" or "slow" position.
Tum the adjusting needle in (clockwise). The en-
gine speed may increase, then it will decrease as
the needle is turned in (lean). Note ttie position of
the needle.
Back the needle out approximately 1/8 to 1/4 tum.
See Figure 6B-4B for best low idle fuel
performance.
6B.4
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