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CARBURETOR TESTING
1. Be wary of fuel leaks! If a fuel leak occurs, stop immediately and repair the
leak. Failure to do so could result in engine fire and serious injury.
NOTE: The following adjustments can affect vehicle emissions. Laws in
your area may govern these emissions.
2. Set idle adjustments per factory recommendations for your vehicle.
3. The choke system is pre-set at the factory. However, minor adjustments
may be required. Adjust using factory specifications for your vehicle.
IDLE MIXTURE ADJUSTMENT
The Edelbrock Performer Replacement Series Carburetor for Q-Jet
applications has conventional Idle Mixture Screws (IMS) that provide a
leaner Air/Fuel (A/F) ratio when turned clockwise and richer A/F ratio when
turned counterclockwise. The idle air flow is controlled by a conventional
screw that opens the primary throttles. The following procedure should be
used to set the idle mixture and speed.
1. Fully warm engine and ensure choke is fully open.
2. Install air cleaner.
3. Set desired speed with the air screw.
4. Adjust the IMS on one side to get the maximum possible rpm or highest
vacuum if you are using a manifold vacuum gauge. Do not go rich beyond
the maximum speed point.
5. If the procedure above changed the idle speed more than 40 rpm, then re-
adjust the idle speed.
6. Adjust the opposite side of that in Step 4 to get maximum rpm or vacuum.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle rpm or manifold
vacuum.
9. Go leaner just enough to get a 20 rpm drop in speed.
10. Reset the speed to the desired rpm.
11. This is a Lean-Best Idle Set. Setting richer than this will not improve idle
quality or performance, but could cause higher hydrocarbon emissions and
tend to foul spark plugs.
12. Emission legal carburetors #1903, #1904 and #1906 are supplied with
tamper resistant protective metal caps for idle mixture screw wells. These
covers should be installed following completion of final idle mixture
adjustments. NOTE: Use idle mixture adjustment tool K&D #2776 or
equivalent.
WINTER FUEL IDLE SETS
During the winter months (in most parts of the country) the local fuel will be
a "winter" blend that is very volatile, as an assist to cold-engine starting
and driveability during warm-up. However, the high volatility has the
disadvantage of allowing excessive vaporization of the fuel if the vehicle is
operated in a heated area such as a garage. This can result in problems in
the idle-set procedures since the carburetor's internal vents will allow this
excess vapor to be drawn into the throats and enrichen the mixture. The idle
will be erratic and not seem to be able to hold a set. To resolve this
problem, it is advisable to perform the final settings outdoors after the
vehicle has been stabilized with a drive of several miles.
FAST IDLE SOLENOID BRACKETS:
Your original Fast Idle Solenoid Bracket should mount to the Edelbrock Q-
Jet Series carburetor. If a replacement bracket is desired, use GM
#7042682 for #1901 and #1902. Edelbrock #1997 is an adapter to connect
a factory vacuum operated throttle kicker to carburetor #1903, #1904 and
#1906.
CHOKE LINKAGE INSTALLATION
The Edelbrock Performer Replacement Series Carburetors for
Q-Jet applications have three different types of chokes; divorced (remote),
hot air, and electric. Figure 3 shows typical divorced choke linkage used
on #1901 and #1902. The metal housing which snaps in place over the
choke coil on manifold has been left off to show choke rod/coil relationship.
The metal housing should be installed on your engine, as it retains the
choke rod in the coil. Stock manifolds can use original equipment choke
© 2002 Edelbrock Corporation
Brochure No. 63-0073
parts, and Edelbrock makes choke linkage kits for use with Performer
manifolds. Use Choke Kit #1931 for small-block Chevy Performers with
divorced choke carbs #1901 & #1902; use Choke Kit #1935 for big-block
Chevy Performers with divorced choke carbs #1901 & #1902. Figure 4
shows typical hot air choke connections as used on carburetor #1903.
Stock manifolds can use original equipment choke parts, and Edelbrock
makes choke linkage kits for use with Performer manifolds. Use Choke
Kit #1930 for small-block Chevy Performers with hot air choke carb
#1903; use Choke Kit #1934 for big-block Chevy Performers with hot air
choke carb #1903. Some OE Q-Jet carbs with hot air chokes use a screw
on nut located at the rear of the choke housing. For these applications,
we recommend the use of the Edelbrock #1932. Some models use
auxiliary vacuum diaphragm on the passenger side rear of carb, remove
the diaphragm and install on the Edelbrock carb.
carburetor #1904 and #1906 require a 12-volt lead that is hot only when
.
the ignition is on
-
Divorced choke
Figure 3
(#1901 and #1902)
Edelbrock Q-Jet Rebuild Kits
The Edelbrock Performer Replacement Series Carburetors for Q-Jet
applications can be rebuilt with the following rebuild kits:
Carb #s
1901 & #1902
1903, #1904 & #1906
Replacement Fuel Filters
The Edelbrock Performer Replacement Series Carburetors for Q-Jet
applications has a replaceable fuel filter element behind the Fuel Inlet Nut.
Replacement filters are available as follows:
Carb #s
1901 & #1902
1903, #1904 & #1906
Q-JET CARBS WITH EGR VACUUM PORTS
The original carb on some Chevy/GMC trucks and Suburbans has the EGR
vacuum port machined higher in the carb venturi than the Edelbrock Q-
Jet. This may have an effect on off-idle performance resulting in a flat
spot. If you get a flat spot off-idle after installing the Edelbrock Q-Jet
carb, you may need to install a vacuum delay valve. A simple test will let
you know if the delay valve is needed: a) Temporarily remove and plug the
vacuum line to the EGR valve. If the flat spot disappears, you will need to
purchase a vacuum delay valve (GM #14020691) and install it in the
vacuum line between the carb and the EGR valve. This valve will delay the
opening of the EGR valve long enough for the carburetor to transition
through the off-idle phase without a stumble, then the EGR circuit will
operate normally.
Note: The vacuum line to the EGR valve should only be removed
temporarily as a test to determine whether the delay valve is
needed. You must re-install the vacuum line to the EGR valve in
compliance with local and/or federal law!
Page 3 of 4
Electric choke
-
Hot air choke
Figure 4
(#1903)
Rebuild Kit #
#1920
#1921
Fuel Filter #
#1970
#1971
Rev 02/02
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