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Automotive Pet Peeves 2: Reader Feedback Is Overwhelming

How many auto repair pet peeves are out there? Well, enough of them that one article wouldn’t hold them all. I’ve received so many emails, texts and phone calls about my article in the February issue that I thought: why not put everyone’s pet peeve...

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Air Filter Show & Tell: Seeing Is Believing

Air filters are normal wear items that ­require regular checks and ­replacement. Their role is to trap dirt particles that can cause damage to engine cylinders, walls, pistons and piston rings. In fuel-injected vehicles, the air filter also plays...

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Searching For 'Black Holes': Job Totals Reveal Missed Selling Opportunities

The concept for Maintenance Chronicle is simple: We ask one shop to record their maintenance sales for a two-week period, and then we see what we learn from the results. This edition of Maintenance Chronicle also proved to be valuable for the shop we...

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MAZDA: Timing Belt & Chain Replacement

This month, we’re going to be looking at the ­timing components on the Mazda line of vehicles. We’ll be focusing on timing belts since they are considered a service item and will present the greater amount of opportunity for replacement. Then, we’ll...

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Honda Element Brake Job

It may look like a car that was never removed from the box it came in, but the Honda Element isn’t boxy when it comes to the brakes. Based on the CR-V platform, there is also nothing tricky when it comes to service. But, its brake system is hardware...

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The Changing Maintenance Market: New Technologies Mean More Opportunities

Most of us wake up each morning, not ­realizing that our professional world has changed even as we slept. Our first job of the day is to service a ­vehicle equipped with an oil life monitor. Not only do we discover that modern oil life monitors can...

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Electronic Proportioning Valve: Doing More With Less Hardware

Anti-lock brake systems (ABS) and the HCU are replacing proportioning, combination and other valves to change the braking forces in the front and rear. This is called Electronic Brake Distribution (EBD) and it can dynamically change the proportioning...

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NHTSA’s GM Brake Line Corrosion Investigation: Reading Between the Brake Lines

There will be no recalls on some GM vehicles for brake line corrosion. Instead, we received an advisory from the National Highway and Traffic Safety Administration (NHTSA) about brake line inspection and car washes. What was not discussed was the corrosion...

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2007-2011 Ford Expedition and Navigator Air Suspension

The Ford Expedition air suspension does more than just lift and raise the vehicle. The system levels the vehicle under loads and when a trailer is attached. The system uses only two air bags on the rear axle unlike previous models with air bags on all...

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Maintaining Your Spray Guns

If there’s one piece of equipment that epitomizes the painter and the paint shop, it’s the spray gun. Over the years we’ve seen many spray guns. Although there are operating principles and functions that remain the same, some have been improved...

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Wheel Bearing Adjustment Tools & Equipment

A recent survey showed that more than half of the bearings on the road today are adjusted incorrectly. A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. An out-of-adjustment bearing affects...

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ETI's ToolTech 2015 Focuses on the Connected Vehicle

ETI’s Annual ToolTech conference remains the premiere event in the tool and equipment industry with more than 115 professionals from over 50 companies in attendance at this year’s ToolTech 2015 in Austin, TX. The Equipment and Tool Institute's...

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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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