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Mazda RX7. Manual - part 32

CARBURETOR - NIKKI 4-BBL

Article Text

1983 Mazda RX7

For www.iluvmyrx7.com

Sunday, August 26, 2001 05:52PM

ARTICLE BEGINNING

1983 Nikki Carburetors
NIKKI 4-BARREL

Mazda RX7

DESCRIPTION

Carburetor is of 4-barrel, 2-stage design. Primary stage
includes idle system, slow speed circuit, accelerator pump system and
main metering system. In addition, Federal models are equipped with a
sub-zero starting device which admits fluid into the primary stage.
Secondary stage contains secondary vacuum diaphragm
operating system, stepping circuit and main metering system. Choking
is accomplished through a semi-automatic choke. Other features
include a deceleration control system, automatic choke return, hot
start assist, idle compensation and dashpot (manual transmission).

ADJUSTMENTS

NOTE: For all on-vehicle adjustments not covered in this article,
see the appropriate TUNE-UP SERVICE PROCEDURES article.

FLOAT LEVEL

1) Before assembling air horn to main body, adjust float
level. Invert air horn and allow float to hang by its own weight.
2) Measure clearance between float and air horn gasket. See
Fig. 1. Clearance should be .61-.65" (15.5-16.5 mm). If not within
specifications, bend float seat to adjust.

Fig. 1: Float Level Adjustment

FLOAT DROP

Turn air horn upright and allow float to hang by its own
weight. Measure distance between bottom of float and air horn gasket.
See Fig. 2. Distance should be 1.98-2.02" (50.5-51.5 mm). If not,

CARBURETOR - NIKKI 4-BBL

Article Text (p. 2)

1983 Mazda RX7

For www.iluvmyrx7.com

Sunday, August 26, 2001 05:52PM

bend float stop to adjust.

Fig. 2: Float Drop Adjustment

CHOKE LINKAGE (FAST IDLE OPENING ANGLE)

Close choke valve fully and measure clearance between
primary throttle valve and wall of throttle bore. Set clearance to
.040-.047" (1.0-1.2 mm) by bending fast idle rod. See Fig. 3.

Fig. 3: Choke Linkage (Fast Idle Opening Angle)
Bend fast idle rod to adjust.

CHOKE VALVE OPENING ANGLE

NOTE: Choke diaphragm No. 1 is the dual diaphragm assembly, choke
diaphragm No. 2 is the single diaphragm assembly.

1) Disconnect both vacuum sensing tubes from No. 1 vacuum
diaphragms. Pull choke lever link out fully and hold in place. Apply
more than 19.7 in. Hg to inner diaphragm. See Fig. 4.
2) Clearance should be .22-.24" (5.5-6.2 mm). Apply more
than 19.7 in. Hg to both diaphragms and measure clearance again.

CARBURETOR - NIKKI 4-BBL

Article Text (p. 3)

1983 Mazda RX7

For www.iluvmyrx7.com

Sunday, August 26, 2001 05:52PM

Clearance should be .45-.51" (11.5-13.0 mm).

Fig. 4: Choke Valve Opening Angle Adjustment

NO. 2 CHOKE DIAPHRAGM

1) Disconnect vacuum sensing tube from No. 2 vacuum
diaphragm. Pull choke lever link out fully and hold in place. Choke
valve should close fully. (Cool bi-metal coil if necessary).
2) Apply more than 19.7 in. Hg to vacuum diaphragm and
measure clearance between choke valve and wall of air horn. Clearance
should be .057-.070" (1.46-1.80 mm).

CHOKE DIAPHRAGM OPERATION (NO. 1 & NO. 2 DIAPHRAGMS)

Remove air cleaner. Start engine and run at idle. Disconnect
both vacuum sensing tubes from No. 1 diaphragm and one from the No. 2
diaphragm. Each diaphragm shaft should move outward from diaphragm.

CHECKING CHOKE DELAY VALVE OPERATION

NOTE: Automatic transmission must be in Neutral.

1) Warm engine to normal operating temperature. Stop engine
and remove air cleaner assembly. Disconnect inner vacuum sensing tube
from choke diaphragm No. 1.
2) Start the engine and run at idle speed. Diaphragm shaft
should move fully inward within 10-20 seconds after reconnecting
vacuum sensing tube to choke diaphragm.

CARBURETOR - NIKKI 4-BBL

Article Text (p. 4)

1983 Mazda RX7

For www.iluvmyrx7.com

Sunday, August 26, 2001 05:52PM

Fig. 5: Checking Automatic Choke Release

CHECKING AUTOMATIC CHOKE RELEASE

1) With engine cold and ignition "OFF", pull choke knob out
fully and release. Knob should return automatically and freely.
Connect tachometer to engine.
2) Start engine and set engine speed at 2000 RPM with choke
knob. As engine temperature reaches range indicated in Fig. 5., choke
knob should return automatically and freely.

CHECKING CARBURETOR HEATER

1) Disconnect electrical connector from No. 1 water
temperature switch and connect jumper wire to both terminals of
connector. Connect tachometer to engine.
2) Disconnect carburetor heater electrical connector and
connect voltmeter to connector. Start engine and set engine speed at
2000 RPM with choke knob.
3) With choke knob pulled out, current should flow to
carburetor heater lead. Current should not flow to heater lead with
choke knob pushed in.
4) Connect ohmmeter between carburetor heater lead and
carburetor body. If ohmmeter shows no movement, carburetor heater is
defective and must be replaced.

HOT START ASSIST CABLE

1) Remove lock spring of hot start assist cable from cable
bracket. Slowly pull outer cable until hot start lever just touches
stop lever.
2) Check clearance between cable bracket and lock nut on
cable. See Fig. 6. Clearance should be .02-.08" (0.5-2.0 mm). Adjust
by turning lock nut, then install lock spring securely on cable.

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