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ASE A5: Brake Fluid and Bleeding Sequence

The ASE A5 Test includes a portion on brake fluid, bleeding, flushing and leak testing. You must know how to: • Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determine needed repairs. •...

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North Dakota Woman Goes From Daycare To Auto Repair

Everyone reading this, raise your hand if you ran a daycare before working in or owning an auto repair shop. Anyone? Well, that’s the story for Elyzabeth Goerger, who was recently profiled in North Dakota’s Prairie Business. Georger is the...

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South Dakota Tech Program Graduates In High Demand

The automotive repair industry, in certain pockets of the country, has a labor force problem. There either isn’t enough technicians to go around, or not enough properly trained technicians to go around. This isn’t the case in Sioux Falls, SD. What...

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Honda: Easy Fix for Engine Noise

We often encounter engines that have a cold-start knock or ticking noise. In this case, the 3.5-L V6 engines installed in various Honda models can make a knocking or ticking noise at idle and only when warm. The cause of the problem is that the rocker...

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Toyota: Rough idle, surging between 500 to 800 RPM

Model: 2005 Toyota Avalon and some models with similar system configurations, such as 2006 Camry models. Condition: The customer ­complains that the check engine light is on, rough idle and engine idle surging between 500 and 800 rpm. The technician...

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Volkswagen: Engine Does Not Start

Vehicle: 2001 Volkswagen Passat GLX, 2.8L Complaint: The customer says the vehicle will not start. Cause: Confirmed the customer’s complaint and found the vehicle did not start. Connected a scan tool and found the following codes: • 17978...

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Electric Power Steering: Past, Present and Future

Electric power steering is fast becoming a standard feature on new vehicles, but it’s not an emerging technology, as it’s been in the field for the better part of two decades. One of the first domestic applications that almost made it to production...

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Are You Chasing Weights?

It has happened to all tire techs, probably more than once. You balance a tire, put the weights on, drop the hood again for a check spin — and the balancer comes up asking for more weight. Fine. You add more weight, drop the hood and...it asks for...

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Cadillac CTS Alignment Spec

The first-generation Cadillac CTS was introduced in 2003 and ended production in the 2007 model year. The Cadillac CTS was built on GM’s rear-wheel drive Sigma platform. The CTS for years 2003-’07 came with two suspension packages­ — standard...

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Midtronics Launches Informational Microsite

  Midtronics, Inc. has launched an informational microsite — or mini website — to provide customers with detailed information about the company’s newest diagnostic platform — the DSS-7000 Battery Service Diagnostic System. The microsite...

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German Tool Specialist KC Tool Announces Addition of Gedore Tools

As of August 1 KC Tool became the first certified reseller of Gedore Tools in the United States already adding more than 2,500 Gedore tools to its selection of German made tools. KC Tool plans to add an additional 6,000 Gedore Tools over the next few...

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United Stationers Expands Into Auto Aftermarket

United Stationers announced Sept. 11 that its wholly owned subsidiary, United Stationers Supply Co., signed an agreement to acquire MEDCO, a U.S. wholesaler of automotive aftermarket tools and supplies, and its affiliates including G2S Equipment de Fabrication...

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Home Engine Diagnostic Dilemmas: Servicing Quadrajet Carburetors

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src=”/wp-content/uploads/Articles/05_01_2008/39766Carb4jpg_00000021239.jpg” border=”0″ ” align=”right” alt=”photo 4: float level can easily be measured on the quadrajet.”/>can be measured by inserting a special Kent-Moore float level gauge into the bowl vent located just aft the choke valve. See Photo 4.

Measuring the distance from the top of the bowl vent to the float and then subtracting the dimension from the bowl vent to the cover gasket can also determine the float level. If a repair manual with adjustment specifications is available, refer to the float level specifications listed for the model number stamped vertically on the driver’s side of the carburetor main body or on a tab attached above the primary throttle shaft. Although most Quadrajet float levels are set at 3/8”, the specification can vary from 5/16” to 1/2”.  Last, the metering rod piston can stick in its photo 5: metering rod travel can be easily checked by inserting an applicable tool into the front float bowl vent. bore, causing a lean air/fuel condition. The metering rod travel can be checked by inserting a screwdriver or punch into the bowl vent hole in front of the choke valve to see if the metering piston spring returns the metering rods to a raised position with the engine off. Spraying some penetrating oil into the bowl vent and tapping on the metering rod hanger with a screwdriver or punch can often loosen the metering rods. See Photo 5.

Quadrajet Adjustments
  The Quadrajet has a number of critical adjustments that make it perform better. The initial adjustment for idle mixture screws on most Q-jets, for example, should be lightly seated and then photo 6: metering rod travel can be easily checked by inserting an applicable tool into the front float bowl vent. backed out three turns. Initial idle speed can be obtained by seating the primary throttle plates and then turning the idle speed screw in about two turns.

photo 7: the secondary metering rod height adjustment should be checked to ensure delivering a correct secondary air/fuel ratio.Primary jetting is most easily corrected by increasing the jet size in two-step increments. To remove the primary metering rods, lightly tap the metering rod hanger with a screwdriver handle. Spring pressure will pop the plastic retainer from the main body casting.

  Before installing any Q-jet, make sure that the secondary throttle plates are seated and that the secondary throttle linkage is adjusted to specification. A tab on the primary throttle shaft actuates the secondary linkage. This tab determines the open position of the secondary plates. When the tab contacts the secondary linkage, the linkage pushes against the upper part of the secondary throttle shaft lever. At that point, the linkage should be located mid-point in the slot located below. See Photo 6.

photo 8: use a 3/32” hex wrench to loosen the lock screw on the air valve spring preload adjustment. On the topside, the secondary metering rod hanger should be adjusted to ideally achieve equal metering rod height and to allow both metering rods to touch the bottoms of their respective wells. This adjustment is done incrementally to avoid binding the rods in their hanger and to avoid damaging the hanger itself. See Photo 7.

 Secondary air valve adjustment is critical to Quadrajet performance because correct secondary air/fuel metering requires a constant depression or vacuum in the secondary venturis. If a repair manual with adjustment specifications is available, begin with the applicable spec. If a specification is not available, preload the air valve spring adjustment one-half turn, Photo 9: Make sure the secondary throttle lockout disengages when the choke valve opens.  then road test the vehicle. If the engine stumbles as it accelerates, increase the spring preload in one-half turn increments until the stumble disappears. See Photo 8.

Last, always make sure that the choke valve lockout is allowing the secondary throttle plates to open. Some Quadrajet models incorporate the lockout at the upper choke housing linkage while others locate the lockout  at the secondary throttle shaft. In either case, the choke valve linkage keeps the air valves closed until the engine warms up. See Photo 9.

Quadrajet Wrap-Up
When serviced correctly, the Quadrajet will prove to be a very responsive and economical carburetor to use for many street driving and racing applications. Although Quadrajet is very dependable, it pays to clean the external choke linkage and air bleeds with an aerosol cleaner. When changing the fuel filter, remember to replace the plastic gasket located on the end of the fuel inlet housing before reinstalling. Cross threading the inlet housing can be greatly reduced by cleaning and oiling the housing threads before installation. If the threads are seriously damaged, aftermarket kits can be used to replace the factory housing. In virtually all cases, a well-maintained late-model Quadrajet will maintain exhaust emissions within legal limits for collector and street rod vehicles while providing a full-bore performance experience.

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Gary Goms

Gary Goms is a former educator and shop owner who remains active in the aftermarket service industry. Gary is an ASE-certified Master Automobile Technician (CMAT) and has earned the L1 advanced engine performance certification. He also belongs to the Automotive Service Association (ASA) and the Society of Automotive Engineers (SAE).
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