15
Emission grade carburetors will have fixed main and
idle circuits. The absence of adjustment screws indicate
fixed jets with no adjustments necessary.
CARBURETOR ADJUSTMENTS
IDLE SPEED ADJUSTMENT
This screw is located on top of the carburetor and
contacts the throttle. To pre-set the idle speed, back
out the screw, then turn in until the screw just touches
the throttle lever. Finally, turn the screw in one (1)
turn. Once the engine is running and brought up to
operating temperature (3-5 minutes), the final idle R.P.M.
can be adjusted with the aid of a tachometer.
FLOAT TYPE-FIXED MAIN, IDLE ADJUST
Turn the mixture adjusting screw in (clockwise) finger
tight, then one (1) turn out (counterclockwise). This
setting is approximate and will be enough to allow
the engine to start so that final carburetor adjustments
can be made. Start the engine and allow it to warm-
up for approximately 5 minutes.
Do not adjust the
carburetor with the engine cold.
NOTE:
If the engine falters or stops after the choke
lever is moved to the "OFF" position, open the mixture
adjusting screw 1/4 turn counterclockwise and restart
the engine.
With the engine running, place the speed control in
the "slow" position. Turn the mixture adjusting screw
clockwise until the engine starts to falter, remember
this location. Next turn the screw counterclockwise
until the engine start to sputter or drops in R.P.M.,
remember this location. Now turn the screw clockwise
until it is halfway between these two locations. This
will be the optimum carburetor setting.
DIAPHRAGM - SINGLE AND DUAL ADJUSTMENT
Turn the mixture adjustment screw(s) clockwise finger
tight, then one (1) turn counterclockwise. This setting
will allow the engine to be started so that the carburetor
can be fine tuned.
Do not adjust the carburetor when
the engine is cold.
Start the engine and let it warm-up for approximately
5 minutes. If the engine falters or stops after the choke
lever is moved to the "OFF" position, turn the adjusting
screw 1/4 turn counterclockwise and restart the engine.
NOTE:
On dual adjust, the first adjustment must be
made with the main mixture screw.
With the engine running, turn the mixture adjustment
screw clockwise until the engine starts to falter,
remember this location. Next turn the screw
counterclockwise until the engine starts to sputter or
drop in R.P.M., remember this location. Now turn the
screw clockwise until it is halfway between these two
locations. This will be the optimum carburetor setting.
With dual adjust carburetor, repeat the above steps
for the second (idle) mixture adjusting screw.
CARBURETOR ADJUSTMENTS
SERIES I
IDLE MIXTURE
SCREW
MAIN MIXTURE
SCREW
SERIES III, IV
IDLE MIXTURE
SCREW
MAIN MIXTURE
SCREW
IDLE MIXTURE
SCREW
MAIN MIXTURE SCREW
F-3
DIAPHRAGM
"F"
DESIGNATION
Summary of Contents for AH520 -
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