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Test Number IB--Carburetor Adjustmentr-M_xture (Atr_Fue!_Ratia_
I.
Rotate the Function Selector Switch to the RPM position.
Slide the
Range switch to the L0-1200 RPM position for idle speed tests.
2.
EMISSION CONTROL SYSTEMS,
Carburetors on late-model vehicles usually
have sealing caps on idle mixture screws which prohibit or restrict
carburetor adjustment. These are factory calibration seals.
Refer
to vehicle manufacturer's service manual for mixture screw adjustment
procedures.
3.
IDLE MIXTURE ADJUSTMENT.
It is adviseable whenever possible to use
the mixture adjustment procedure as outlined in the manufacturer's
service manual.
The following procedure should work well, however,
on those vehicles without emission control systems.
Turn the idle
mixture screw in (lean) until the idle RPM starts to decrease and the
engine begins to idle roughly.
When this point is reached slowly back
the idle mixture screw out (rich) until the maximum steady RPM is obtained.
When making any mixture adjustment only turn the mixture screw i/8
of a turn at a time.
Between adjustments allow about 30 seconds for
the engine speed to stabilize.(Figuro 40)
4.
MULTI-BARREL CARBURETORS,
Repeat procedure described in Test Number
3 on EACH mixture screw until the smoothest maximum RPM is obtained.
Turn each screw i/8 of a turn at a time to prevent engine stalling.
If the final idle RPM is now higher than specified, readjust mixture
screws again until no further increase is possible.(Figure 4))
5.
NOTE:
On vehicles with emission control systems, air injection pumps
and positive crankcase ventilation, refer to vehicle tune-up decal in
the engine compartment for idle adjustment procedures.
IMPORTANT! Air/Fuel mixture adjustment is one of the more critical adjust-
ments on the engine,
Fuel economy and Emission Control can be diminished
through incorrect settings or adjustment,
Carefully follow the vehicle
manufacturer's instructions when adjusting carburetor idle mixture.
Curb Idle Speed
Adjustment
TYPICAL,SINGLE
AND
MULTIPLE
BARREL
CARBURETORS
Idle
Mixture
Screw
Anti-Dieseling
Solenoid
Idle
_ixture
Screws
FIGURE 40
FIGURE 41
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