I need help tuning my quadrajet!?!?!?!?

Question

Does anyone REALLY know how to tune a quadrajet? I need help!?
I just had a 383 stroker built for my 68 chevelle malibu. I put an edelbrock torquer manifold on it but dont have the money yet for a new carburator. But I already have a near new Rochester Quadrajet rebuilt by Holley. I would like to know how to adjust the fuel/air ratio PROPERLY. If anyone knows any tricks and/or methods or know where I can find specs on how to do this please help.

Answer 1

The great thing about QJ's is that they are "demand" carbs and really self adjusting for the most part.

If you're sure you have the correct primary and secondary jets for your application, and the idle mix is correct... here's the (very) long version on how to tune a QJ:

How to Tune a Q-Jet


Overview
The Rochester QuadraJet, in its various forms and configurations, has been used by various GM Divisions for various applications since the mid sixties. The last passenger car version of the carb appeared as an ECM-controlled carb in 1981.

The Q-Jet is a highly versatile, tunable carb that will provide outstanding performance and reliability once set up correctly. This paper will discuss the tuning and setup, and will provide you with adequate data to make good decisions when jetting and adjusting the carb. This paper will not discuss basic rebuilding sequences, nor will I discuss operations involving machining operations and other severe alterations to the carb. There are many books on the market that deal with these subjects in depth. Rather, I will describe the various systems, their purpose, and a good tuning sequence to help you get each system and parameter set up correctly in the easiest way possible.

QuadraJet carbs have three basic tuning variables, and these get people all confused: Primary Metering Jet, Primary Metering Rod, and Secondary Metering Rod. Attempting to cure problems by tuning the wrong variable results in lots of frustrations for tuners and car owners.

These systems at times overlap in their operation. Not only does each system need to be properly tuned, but its timing and “overlap” with other systems is critical to proper performance.

When tuning, we think of each of these variables as controlling a different operating range: The primary jet size determines the fuel mixture at Wide Open Throttle (WOT). The primary metering rod determines fuel mixture at cruise speed and determines responsiveness of the idle mixture screws and off-idle performance. The secondary rods are a high-rpm compliment to the primary side, and are used for final “tweaking.”

On a Q-Jet, we see that we can control the fuel mixture throughout the operating range. This is different from a Holley: A Holley has a given main jet size which meters fuel throughout the rpm range, including cruise. At WOT, the power valve unseats, and opens a fixed orifice, dumping a fixed amount of fuel in addition to the main jet. Crude, but simple and effective.

The Q-Jet meters fuel through the main jets. Metering rods, suspended from a power piston, “plug off” part of the area of the main jets by being inserted into the jets. These rods have a “fat” diameter and a “skinny” diameter: The number stamped into the side of every metering rod is the “fat” diameter indicated in thousands of an inch. This part of the rod is pulled into the main jet at cruise, at idle and at other high-vacuum operating conditions (light throttle). It produces a lean operating condition for good fuel economy and good throttle response. When engine vacuum is lost, indicating a high-power condition, the rods are pushed out of the jets by spring pressure, and only their “skinny” tips, or power tips, remain in the jets. This richens the fuel mixture up for peak power. All primary metering rods have the same power tip diameter (.026”). This fact is crucial to remember when tuning: Primary metering rod sizes have no effect on WOT performance.


Identification

Q-Jets are identified by a number stamped into the Float Bowl casting on the driver’s side of the car just above the secondary throttle linkage. If the carb is a Carter manufactured under license froom Rochester, the number will be inside a round metal foil tag on the driver’s side of the carb just above the primary throttle linkage.



Metering Area

WOT fuel mixture is controlled only by the main jet size. Performance at cruise and at idle is then controlled by the rods. We can establish each of these mixtures independently of the other by knowing and understanding the concept of Metering Area.

Jet and rod sizes are always referred to by their diameter in thousands of an inch. But fuel flow doesn’t “see” diameters: The fuel “sees” the total metering area. So we must convert the diameter into a resulting area. We remember that the formula for area is r2. Thus a jet with a diameter of .070” has a metering area of:

Radius = ½ diameter

Radius = .035”

.0352 = .00384”

Thus, the metering area of a #70 jet is 3.84 thousands of a square inch.

But wait! There is a rod inserted into the jet, so we must subtract the area of the rod. Let’s say we have a #40 rod in that #70 jet. The area of the rod is:

Radius = ½ diameter

Radius = .020”

.0202 = .00125”

Thus, the area that a #40 rod “plugs off” is 1.25 thousands of a square inch.

The resulting metering area of the #70/#40 combination is thus 3.84 minus 1.25. The total metering area is 2.59 thousands of a square inch. This is the metering area of this rod/jet combination with the rod fully inserted in the jet. In other words, this is the metering area at cruise speed and at idle.

To see the metering area at WOT, we know that all rods have a .026” diameter power tip. So we run the same calculation for a .026” diameter rod inserted in the jet.

It is these numbers that we will use in all comparisons when making jet changes. We will use these numbers also to look at the percent differences in jet changes.

So that you won’t need to run around with a calculator, my Carb Listing in Table 1 shows the metering areas for every carb listing at both cruise and at WOT. The number is the metering area in thousands of an inch for a single jet/rod in the carb. This number is effectively how rich/lean the carb is really jetted, and you can directly compare these numbers to see how the various carbs were set up by the factory. By dividing one area into another area, you can see the percentage difference in the jetting.

Figure 2 is a table showing you what the metering area is for every possible jet/rod combination. Each grouping of jets starts off with the rod power tip diameter of .026” so you can see the WOT metering area of that jet size. It then jumps to the first usable rod size.

Tech Tip #1
Before you go trying to fix all the errors of the previous carb tuner, set your carb up to the stock spec for your carb part number. A carb jetted and set up to its stock specs will usually run pretty good on just about any application, and this gives you a good starting point. From there, you can start doing refinements as outlined in this paper.

The carb number on a Q-Jet is usually stamped into the bowl casting on the driver’s side of the carb in the area above the secondary throttle shaft. The number starts with either “70…” or “170…”. If the carb is a Q-Jet manufactured under license by Carter, it will sometimes have the carb number stamped into a foil circle on the driver’s side of the bowl just above the primary throttle shaft.

The carb listing (Figure 1) is a partial listing of popular Pontiac and Chevy Q-Jets that I have compiled over the years. It is not a complete listing of every carb used by Chevy or Pontiac. Most notably, I have very few of the truck carbs listed, yet there are many truck carbs running around on passenger cars.

Tech Tip #2
What has a greater effect on performance: primary or secondary jetting? I constantly see people swapping around secondary rods, trying to get the best performance out of their cars. The secondary rods are very easy to change, and since the secondaries are so BIG, the secondary metering has to be the most important, right?

Wrong.

Most Q-Jets are 750 cfm carbs. This is more airflow than most small block engines can ever handle. Yet, GM used Q-Jets on everything from Overhead Cam 6-cylinder Pontiacs and Corvair 6-cylinders, to 500 cube Caddys. How?

The secondary airvalve on the Q-Jet effectively makes the Q-Jet a variable-cfm carb. The spring windup of the airvalve combined with the bleed-off of the choke pulloff diaphragm allow the secondaries to open only as much as the engine can handle. Thus, if the engine can’t handle all of the cfm, the secondaries simply don’t open all the way.

The primary side, however, is used throughout the rpm range. It is always in use, and provides the metering for the majority of the power produced by the engine. Let’s look at the scenario:

You’re at the stoplight. You bring the rpm up slightly against the torque converter – 1500 rpm. You’re on the primary side of the carb only, and this is what is producing all of your torque right now. The light changes, and you put the pedal to the metal. All of your torque at launch is being produced by the primaries only, as the secondaries don’t see enough airflow to open. The rpm comes up quickly: 2000, 2500, and now the secondaries might be starting to crack. Almost all of the air is still passing through the primaries, and the secondaries are now starting to compliment it just a tad. 3000, 4000 rpm, and the secondaries might be half-way open. The primaries are still providing most of the airflow and metering. 5000, 5500 and you hit redline just as the secondaries hit about ¾ open. Second gear, your rpm drops, partially closing the secondaries back up, and you’re back to sucking the majority of the air through the primaries once again.

So we see, the secondaries provide only a compliment to the primaries. The primaries provide the vast majority of the fuel metering, and primary jetting is absolutely the most critical to proper performance. You cannot compensate for poor primary jetting by re-jetting the secondaries. So we are going to concentrate on jetting the primary side for peak performance, and then we will set up the secondary side to provide a proper compliment to the correct primary jetting.

Tech Tip #3
How can you tell if an off-idle stumble is caused by a lean or a rich condition?
A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. I actually use a small, broken drill bit that’s just the right size. Using a hammer, gently tap the roll pin in towards the choke air horn wall. Don’t jam the pin right up against the wall: Leave just a little bit of a gap so you can get a screwdriver blade in between the wall and the pin to pry it back again. With the pin tapped out, remove the accelerator pump lever. I like to do this with the engine running so I won’t have any trouble starting the engine without the accelerator pump. Now, rev the engine a little with the throttle. Notice if the engine seems quicker and more responsive, or if the hesitation & stumble is worse. If the engine actually feels more responsive with the accelerator pump disconnected, you have a rich condition. If the hesitation is worse than before, you have a lean condition. If there is no change whatsoever, you have a non-functional accelerator pump.

To verify a suspected lean condition after this test, simply hold your cupped hand lightly over the choke air horn area with the engine running at idle, restricting the air flow. If the idle speed and idle quality momentarily increases, you have a verified lean condition. You need to select a jet/rod combination that will give you a little more Cruise Metering Area. Make these changes in less than 10% increments using the Figures provided in this paper.

Tech Tip #4
How can you tell if your power piston spring is too stiff and not allowing the power piston to “seat” at idle?
If your engine does not produce enough manifold vacuum at idle and/or cruise (due to a lumpy cam or other engine parameters), it is possible that the power piston is not being pulled all the way down to its seated position due to the power piston spring being too stiff. The result is that the car will run very rich at idle, and the idle mixture screws will have little effect or response. Idle speed may also “float,” with idle speed starting high and gradually decreasing until the engine stalls due to the engine getting “loaded up.” There will typically be a puff of black smoke out the tailpipes when you “flick” the throttle.

To test for this, pop the top off the carb, remove the power piston/rod assembly, and remove the power piston spring from its bore. Re-install the rod/piston assembly without the spring and put the carb back together. The carb will now run in the full-lean condition all the time. If this clears up the idle, improves idle mixture screw response, and eliminates the black smoke when you flick the throttle, you need to install a softer spring. Edelbrock has a complete power piston spring assortment available.

Tech Tip #5
How can you tell how stiff the power piston spring needs to be, and how can you tell one spring from another?

If you have a few springs of various kinds laying around, it is not readily apparent which spring is stiffer than another. You can arrange them and order them from softest to stiffest as follows:

Using your carb, or a junk float bowl from another carb, as a testbed, remove the carb air horn (the “top” of the carb) and remove the power piston and its spring. Remove the primary metering rods from the piston. Now, drop a spring into the power piston bore and install the piston. Find a Phillips screwdriver, and place the handle of the screwdriver on top of the power piston with the shank of the screwdriver pointing straight up. Use a screwdriver that is light enough to NOT compress the power piston and its spring, but close. Now, drop flat washers onto the shank of the screwdriver and keep stacking them up until the piston compresses the spring and seats in the bore. Count the number of washers it took to compress the spring and label the spring as a “6-washer spring,” for instance. Do the same with the other springs you want to test. You’ll end up with a comparative rating of springs, like “4-washer,” “6-washer,” or “10-washer” springs. You now know exactly how to arrange them from softest to stiffest.

But which one should you use? You’ll need a junk Q-Jet float bowl for this test, and you’ll need to have your engine in running condition.

Using a stripped down, bare Q-Jet float bowl, you’ll notice that there is a hole in the bottom of the bowl right underneath the power piston bore. This is the vacuum hole that applies manifold vacuum to the power piston. Hook up a long vacuum hose to a manifold vacuum source on your engine. Now, install a power piston spring from your arranged spring selection into the piston bore and install a power piston on top of the spring. Start your engine, and stick the end of the vacuum hose onto the hole in the bottom of the stripped down float bowl. With the engine at idle, the vacuum applied to the bowl should immediately pull the power piston down against the spring pressure and seat the power piston firmly in its bore. If the piston does not fully seat, you need a softer spring from your arranged spring selection. If you have an automatic, put the transmission in “drive.” Make sure the power piston stays seated.

If you really want to do some testing, you can string the vacuum hose into the car, and with an assistant, drive the car around and observe under what conditions the power piston starts to unseat: While you drive, have the assistant stick the vacuum hose onto the bottom of the bowl, and observe what the piston does under various engine loads. Make sure you have a spring that’s stiff enough to make the piston pop up when your engine is under load, yet soft enough to keep the piston fully seated at idle, at cruise and under light acceleration. This makes for some really fun testing, and the results will pay off in a precisely matched power valve spring for some outstanding throttle response.

Of course, if you buy the power piston spring assortment kit from Edelbrock, the springs will be identified and labeled as to their vacuum rating. Select and use a spring with a rating about 1.5” to 2” lower than the idle vacuum of the engine (in drive).

Tech Tip #6
The idle metering circuit on a Q-Jet is not an independent, stand-alone circuit. The idle mixture screws in the throttle plate receive their fuel through the main metering jets. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. The idle mixture screws cannot meter more fuel than the main jets/rods will allow. Thus, if your Cruise Metering Area jet/rod combination is too lean, you may find that your idle mixture screws are ineffective. If your idle surges, is rough & unstable, and adjusting the screws seems to make no difference (but you can kill the engine by turning them all the way in), chances are good that your cruise metering area is too lean. You can verify this by running your mixture screws out to the point where additional turns have no effect on idle. Then cover the choke area of the carb with your hand. If idle speed & quality increases as you restrict the air flow, your jet/rod combination is too lean.


Procedure
Here is my recommended sequence and procedure for doing a basic Q-Jet set-up:

1. Set the float level.
You’ll be amazed how many people try tuning a Q-Jet without ever checking the float level. An incorrect float level can give you all kinds of symptoms and problems, so get this one set right off the bat.

You have to pull the top of the carb off to set the float level. With the top removed, remove the big phenolic spacer that covers the area around the needle/seat. Hold the float hinge clip firmly seated and push down lightly on the float where it contacts the needle. Measure from the top of the float bowl to the top of the float at the rear edge of the float. Float level should be .375” - .400” for a street-driven car. Adjust by removing the float and bending its lever arm. Never raise the float level by forcing the float against the needle/seat to bend it – this will damage the needle.

2. Determine main jet size.
If you have a stock engine, always start with the stock jet size and work from there. If you have the typical street modifications like headers, good exhaust system and a free-flowing intake, you can start with a main jet size 2 sizes larger than stock.

Since we want to work on the primary side only, we don’t want the secondaries interfering with the jetting process. Chevy Q-Jets have a secondary lockout lever on the passenger side of the carb right at the secondary throttle shaft. This lever is actuated by the choke linkage, and prevents the secondaries from opening when the engine is cold. I call this the “primary jet tuning lever.” Use a piece of wire or string to engage the lever with the secondaries so that the secondaries cannot be opened.

You now need to find a short flat stretch of road to test drive the car. You need to be able to measure time-to-distance and/or speed-at-distance. I usually find a repeatable stretch of road about 300 feet long. This gets me through 1st gear and into 2nd. Make two or three runs on the car through this stretch and make note of time and speed to distance. Also note the seat-of-your-pants feel of the car (it’s going to feel pretty slow with the secondaries locked out…).

I recommend making jet changes in less than 10% increments. Go to Figure 2 and determine your WOT metering area for your current jet size. This will be the metering area of the jet with the .026” rod. With this number, go to the Jet % Change Chart and find the closest metering area match in the left vertical Metering Area column (Use the “Area” column and not the Jet Size column. The Jet Size column can only be used on carbs that do not employ a metering rod, such as Holley and Weber.). Follow the row across until you get into the “green” zone and find the closest number to 10%, but not greater than 10%. Now go straight up until you get to the new metering area number. This is your target. Take this number and go back to Figure 2 and find the closest jet size that will produce this metering area with a .026” rod. This is the first jet size you want to try, and this will increase your fuel mixture by the percentage indicated in the chart.

Now, to keep your off-idle mixture unaltered, you also need to check your cruise metering area. Go to Figure 2 and find your old main jet & rod combination. Note the resulting metering area for this combination. Now, go to your new main jet size that you’re going to be using and find the rod needed to produce the same cruise metering area you had before. Use this rod with the new jet.

By doing this, you are now changing only 1 parameter at a time: WOT mixture only. Idle, off-idle, and everything else is now unchanged, and you will be able to see the results from the mixture change at WOT only. With the secondaries still locked out, run the car 2 – 3 times down the same stretch and record results. If the numbers get better, you’re going the right way with the main jet size. If the numbers are worse, you need to make changes to the lean side instead of rich. Repeat this operation until you determine the main jet size that produces the best numbers. On many stock cars, you may be surprised to learn that you end up with the stock jet size. You have now optimized main jets.

3. Determine main metering rod size.

NOTE: There are two different “series” of primary metering rods. Q-Jets up through 1974 (the “4MV” series carbs) use the early series rods, also known as the “single taper” rods. 1975 and later Q-Jets (the “M4M” series carbs) use the second series rods, also known as the “double taper” rods. Not only do the rods differ in their taper design, but they are different lengths. You cannot interchange the two different rod series.

When switching main jets around, you were also swapping out metering rods to keep the cruise metering area unchanged. You did this to make sure that your off-idle throttle response remained unchanged so that the throttle response off idle did not affect the tuning results from the main jet re-sizing. Now, with your new main jets, your cruise metering area is exactly the same as it was before, but that’s not to say it’s right.

There are several indicators of correct cruise metering area. First, check out Tech Tip #5 regarding the idle circuit. This is a good indication of a lean condition. But here’s another good indicator of correct cruise metering area:

A Q-Jet, when set up with the correct metering rod for cruise & idle, will produce a slight hesitation upon acceleration if the accelerator pump is disconnected. Using a small pin punch or a finish nail, carefully knock out the roll pin securing the accelerator pump arm to the top of the carb. I do this with the engine running so I don’t have any trouble starting the engine without the accelerator pump. With the pump disconnected and with the engine running in neutral, “flick” the throttle just a little. If the engine actually feels more responsive with the pump disconnected, your cruise metering area is too rich, and you need to install a fatter set of rods. If you get a severe stumble, or if the engine dies, you’re on the lean side and need smaller rods. When the rods are correct for the jets in use, you will get a slight hesitation when the pump is disconnected.

Once you have set the rod size up like this, verifying both the idle as shown in Tech Tip #5 and using the disconnected accelerator pump, a road test is in order. If the car is a little “flat” on light acceleration, or if it has a slight “surge” at steady cruise, you need to richen up the metering area slightly. If it is smooth and responsive on light acceleration, and feels smooth at cruise, you have the rod size nailed down.

Again, use the charts to keep all changes limited to 10% at a time. This will prevent you from “over-shooting.” Remember, with the main jet size determined, your rod sizing is affecting idle, off-idle, light acceleration, and cruise. In most cases, when there are problems with stumbles, poor idle, and surging at cruise, the rods are too big and are causing a lean condition. On the other hand, if the rods are too small, causing a rich condition, the throttle will feel “lazy” or “slow” when you rev the engine, and you may get a puff of black smoke when you “flick” the throttle. Correct rods will produce crisp, clean and instant throttle response.

4. Determine secondary rod size.
You are now finally ready to unlock the secondaries. But before you start changing the rods, you want to get the secondary opening rate set up. This is determined by the spring windup.

It is a very common “speed trick” to loosen the secondary windup spring so that the secondaries will open very quickly. This is the single most common cause of a severe stumble or hesitation upon acceleration or transition into the secondaries.

The secondary spring windup is adjusted with a small, slotted-head screw on the passenger side of the carb, right at the top of the carb on the secondary side. The screw head points right out to the side. 90 degrees from this, on the bottom, there is an allen-head lock screw that keeps the slotted screw from turning. If you have trouble seeing it, place a mirror under the area until you spot it. With a small slotted screwdriver holding the adjustment screw, loosen the allen screw about ¼ turn. This will allow you to turn the slotted adjustment screw. Counting the turns, allow the slotted screw to slowly unwind until all spring tension is gone. You can use your mirror to see the spring disengage contact from the pin lever underneath the air horn. If the spring tension was lost after only ½ turn, the windup was too loose. Bring the spring into contact with the lever. Note when it just barely touches. From this point, wind the spring up between ¾ turn and 7/8 turn. This is a good starting point, and will prevent any bogs or hesitations due to premature secondary opening.

Now, you need to adjust the secondary rod hanger height. You’ve read all about the different letter numbers for the secondary hangers, and how a “Y” hanger will make your car faster than an “M” hanger or whatever. Fact is, you can bend and adjust any hanger to any hanger height you want, so it doesn’t make a heck of a lot of difference what hanger you choose to use. Just get it set up right:

With the secondary airvalve held wide open and the secondary rods pulled all the way up, measure the distance from the top of the rear wall of the choke horn to the secondary rod hanger hole in the hanger. This distance should be 41/64”. Bend the hanger to adjust – you have to adjust each of the two sides independently. You now have a “performance” rod hanger.

With this set, you can now play with secondary metering rods. A common speed trick mistake is to always install thinner (richer) secondary rods. Some engines and carbs will produce a secondary “lag” if the rods are too thin. On about half of the engines I work on, I obtain better performance by installing fatter “non-performance” rods. Again, a quick road test is the only way to set this up, so go back to your 300-foot stretch and make a few runs with rods both richer and leaner. Once you have found the rods producing the smoothest secondary transition and the best numbers, you can start unwinding the secondary airvalve spring. Relax the spring tension in 1/8 turn increments until the car stumbles on acceleration, then tighten up 1/8 turn again. You have now determined the quickest secondary opening rate that your engine can handle, and your secondary mixture is set.

Note that secondary metering rods come in three different tapers: long tip, short tip, and medium tip (see Figure 3). Most of the available after-market metering rods have the long tips, and these will produce a full-rich mixture upon the slightest opening of the secondaries. Many street engines will produce better performance by using the short tipped rods. A short tipped rod does not allow a full-rich mixture until the secondaries are opened quite a ways, keeping the mixture a little lean initially. This can produce smoother and crisper performance in many applications. Next time you see a junk Q-Jet laying around, make sure you yank the rods and jets out of it: many old truck carbs have some really good short-tipped secondary rods in them. Figure 3 lists all the secondary rod letter codes, part numbers, and measurements.


Parts
If you don’t have a stash of used Q-Jets in your basement to rob jets and rods out of, you can get parts from Edelbrock. Youlocal parts store should be able to order them for you. Following is a partial listing of Edelbrock Q-Jet parts and part numbers:

Primary Metering Rods (pairs) for 1974 & earlier:

.035”#1936.039”#1939.043”#1944
.037”#1937.041”#1942.045”#1946

Primary Metering Rods (pairs) for 1975 & later:

.048”#1941.052”#1945
.050”#1943.054”#1947

Secondary Metering Rods (pairs) for all years:

CC#1950CK#1952CL#1954
CE#1951AY#1953

Primary Metering Jets (pairs) for all years:

.068”#1968.072”#1972.076”#1976
.069”#1969.073”#1973.077”#1977
.070”#1970.074”#1974
.071”#1971.075”#1975

Questions, Comments & Technical Assistance
If you have questions or comments regarding this article, or if you notice any errors that need to be corrected (which is quite possible since I’m writing this from memory…), please feel free to drop me an e-mail. Also, if you need any technical assistance or advice regarding this process, or other maintenance issues, feel free to contact me:

[e-mail]


Figure 1: Carb part number listing & stock jetting

Carb #ApplicationMain JetMain RodSpringSec. RodJet AreaJet Area
(1 Jet, .001")(1 Jet, .001")
CruiseWOT

7027262Pont 67 400 AT & MT GTO70417002071BF2.52823.3175
7027263Pont 67 400 MT w/o A.I.R.70397002071BF2.65393.3175
7028262Pont 68 400 STD AT73437037305BE2.73323.6545
7028263Pont 68 400 MT GTO72407037305BE2.81493.5406
7028267Pont 68 400 H.O. MT GTO72417037305BE2.75123.5406
7028268Pont 68 400 & 400 H.O. AT GTO73427037305BE2.79993.6545
7028268Pont 68 GTO Best Tuned Condition71427037305DA2.57373.4283
7028270Pont 68 400 RAM AIR AT after Jan 6872417037305BE2.75123.5406
7028270Pont 69 400 AT RAM AIR III72417037305BE2.75123.5406
7028273Pont 68 400 RAM AIR MT after Jan 6872427037305BE2.68613.5406
7028273Pont 69 400 MT RAM AIR III72427037305BE2.68613.5406
7028274Pont 68 400 AT EARLY RAM AIR73417037305BE2.86513.6545
7028275Pont 68 400 MT EARLY RAM AIR72407037305BE2.81493.5406
7029263Pont 69 400 MT GTO71447037305BE2.43873.4283
7029268Pont 69 400 AT GTO71447037305BE2.43873.4283
7029270Pont 69 400 AT RAM AIR IV69387037305BP2.60523.2084
7029273Pont 69 400 MT RAM AIR IV69377037305BP2.66413.2084
7037262Pont 67 400 AT w/A.I.R. GTO70407002071BF2.59183.3175
7037263Pont 67 400 MT w/A.I.R. GTO70387002071BF2.71433.3175
7037271Pont 67 400 RAM AIR after 6 Feb 6770387002071BF2.71433.3175
7040263Pont 70 400 MT FEDERAL GTO71447037305CC2.43873.4283
7040264Pont 70 400 AT FEDERAL GTO70417037305BP2.52823.3175
7040267Pont 70 455 MT FEDERAL GTO71427037305CC2.57373.4283
7040268Pont 70 455 AT FEDERAL GTO71427037305CC2.57373.4283
7040270Pont 70 400 & 455 RAM AIR AT GTO70397037305CC2.65393.3175
7040273Pont 70 400 & 455 RAM AIR MT GTO70397037305CC2.65393.3175
7040563Pont 70 400 MT CALIFORNIA GTO68367037305BU2.61383.1008
7040564Pont 70 400 AT CALIFORNIA GTO68387029922BU2.49763.1008
7040567Pont 70 455 MT CALIFORNIA GTO70407029922BU2.59183.3175
7040568Pont 70 455 AT CALIFORNIA GTO69377029922BU2.66413.2084
7040570Pont 70 400 & 455 RAM AIR CALIF.67337037305CC2.67042.9947
7040573Pont 70 400 & 455 RAM AIR MT CALIF.67337037305CC2.67042.9947
7041262Pont 71 455 AT GTO71437037305BU2.50703.4283
7041263Pont 71 400 MT GTO75477037305BU2.68293.8869
7041264Pont 71 400 AT GTO71467037305BP2.29733.4283
7041267Pont 71 455 H.O. MT GTO73387037305BP3.05133.6545
7041268Pont 71 455 H.O. AT GTO74437037305BP2.84863.7699
7041270Pont 71 455 AT RAM AIR74437037305BP2.84863.7699
7041273Pont 71 455 MT RAM AIR73387037305BP3.05133.6545
7041273Pont 71 455 H.O. Best Tuned Condition72387037305BP2.93743.5406
7042262Pont 71 455 AT CALIFORNIA72437037305CR2.61933.5406
7042263Pont 72 400 MT GTO72457037305CS2.48113.5406
7042264Pont 72 400 AT CALIFORNIA74477037305CR2.56593.7699
7042270Pont 72 455 H.O. AT71457037305CR2.36883.4283
7042272Pont 72 455 AT GTO72437029922CR2.61933.5406
7042273Pont 72 455 H.O. MT71437037305CR2.50703.4283
7042273Pont 73 455 S.D. MT Early71437037305CR2.50703.4283
7042274Pont 72 400 AT FEDERAL74477029922CS2.56593.7699
7042276Pont 72 455 AT HI ALTITUDE71437037851CR2.50703.4283
7042278Pont 72 400 AT HI ALTITUDE72467037851CS2.40963.5406
7043262Pont 73 455 AT71417029529CR2.63893.4283
7043263Pont 73 400 MT71437037851CS2.50703.4283
7043264Pont 73 400 AT72437029529DB2.61933.5406
7043266Pont 73 400 LATE AT72457029529DB2.48113.5406
7043270Pont 73 455 S.D. AT76517029529BV2.49364.0055
7043272Pont 73 455 AT HI ALTITUDE70417029529CR2.52823.3175
7043273Pont 73 455 SD MT75497029529BV2.53213.8869
7043274Pont 73 400 AT HI ALTITUDE72457037851DB2.48113.5406
7044266Pont 74 ALL AT72457029529DB2.48113.5406
7044268Pont 74 350 AT72437029529DB2.61933.5406
7044269Pont 74 350 MT68357037851DB2.66963.1008
7044274Pont 74 ALL HI ALTITUDE72457037851DB2.48113.5406
7044568Pont 74 350 AT CALIFORNIA72437029529DB2.61933.5406
17054910Pont 74 455 SD Replacement75497029529BV2.53213.8869


7025200Chev 65 396 AT EARLY714470312082.43873.4283
7025201Chev 65 396 MT EARLY714170312082.63893.4283
7025220Chev 65 396 AT LATE714470312082.43873.4283
7025221Chev 65 396 MT LATE714470312082.43873.4283
7026200Chev 66 396 AT71447029862AX2.43873.4283
7026201Chev 66 396 MT71417029862AX2.63893.4283
7026202Chev 66 327 AT EARLY71457029862AK2.36883.4283
7026203Chev 66 327 MT71437029862AK2.50703.4283
7026204Chev 66 427 AT71467029862AX2.29733.4283
7026205Chev 66 427 MT71417029862AX2.63893.4283
7026210Chev 66 327 AT LATE71457029862AK2.36883.4283
7027200Chev 67 396/427 AT W/O A.I.R.71447029862AX2.43873.4283
7027201Chev 67 396/427 MT W/O A.I.R.71417029862AX2.63893.4283
7027210Chev 67 396/427 AT71447029922AX2.43873.4283
7027211Chev 67 396/427 MT71417029922AX2.63893.4283
7028207Chev 68 327/350 MT VETTE71467029862AN2.29733.4283
7028208Chev 68 327/350 AT VETTE71467029862AN2.29733.4283
7028209Chev 68 427 HIGH PERF MT VETTE71457029862AX2.36883.4283
7028212Chev 68 327/350 AT71467029862AN2.29733.4283
7028216Chev 68 427 HIGH PERF AT VETTE71477029862AX2.22423.4283
7028217Chev 68 396 HIGH PERF MT VETTE71457029862AX2.36883.4283
7028218Chev 68 396 HIGH PERF AT VETTE71477029862AX2.22423.4283
7028219Chev 68 HIGH PERF MT VETTE66367029862BG2.40332.8903
7028229Chev 68 HIGH PERF MT CHEVY II66367029862BG2.40332.8903
7029202Chev 69 350 300HP AT VETTE67427029862AN2.14022.9947
7029203Chev 69 350 300HP MT VETTE67387029862AN2.39152.9947
7029207Chev 69 350 325HP VETTE66367029862BG2.40332.8903
7029215Chev 69 396/427 MT71457029862AX2.36883.4283
7037200Chev 67 396/427 AT A.I.R.71467029862AX2.29733.4283
7037201Chev 67 396/427 MT A.I.R.71417029862AX2.63893.4283
7040207Chev 70 350 FEDERAL VETTE76447029862BA3.01594.0055
7040503Chev 69 350 300hp SS Camaro76447036019BA3.01594.0055
7040503Chev 69 350 300hp Best Tuned74437037305AK2.84863.7699
7040507Chev 70 350 CALIFORNIA VETTE76447029862BA3.01594.0055
7041204Chev 71 454 AT VETTE77497029862BG2.77094.1257
7041205Chev 71 454 MT VETTE77497036019BG2.77094.1257
7041205Chev 71 454 MT VETTE77497029862BG2.77094.1257
7041212CHEV 71 Vette 350 A/T74447029862AR2.78033.7699
7041213CHEV 71 Vette 350 M/T74447029862AR2.78033.7699
7042203CHEV 72 Vette Fed M/T 35074457029862DA2.71043.7699
7042216CHEV 72 Vette A/T 45477497029862CM2.77094.1257
7042217CHEV 72 Vette M/T 45477457029862CM3.06624.1257
7042902CHEV 72 Vette Fed A/T 35074457029862DA2.71043.7699
7042903CHEV 72 Vette Calif. M/T 35074457029862DA2.71043.7699
7043200CHEV 73 454 all Auto77507029862DA2.69314.1257
7043201CHEV 73 454 all M/T77487029862DA2.84714.1257
7043202CHEV 73 350 all Auto73447029862DA2.66493.6545
7043203CHEV 73 350 all M/T73447029862DA2.66493.6545
7043212CHEV 73 Vette Hi Perf. Auto74447029862DA2.78033.7699
7043213CHEV 73 Vette Hi Perf. M/T74447029862DA2.78033.7699
7044206CHEV 74 Vette & Nova Fed A/T75467029862CH2.75603.8869
7044207CHEV 74 Vette & Nova Fed M/T75467029862CH2.75603.8869
7044208CHEV 74 350 Camaro Hi Perf. A/T75437029862DA2.96573.8869
7044209CHEV 74 350 Camaro Hi Perf. M/T75437029862DA2.96573.8869
7044210CHEV 74 Vette 350 Hi Perf. M/T75437029862DA2.96573.8869
7044211CHEV 74 Vette 350 Hi Perf. A/T75437029862DA2.96573.8869
7044506CHEV 74 Vette & Nova Calif. A/T75467029862CH2.75603.8869
7044507CHEV 74 Vette & Nova Calif. M/T75467029862CH2.75603.8869
7045200Chev 75 454 AT Chevelle/Monte76437041477CJ3.08434.0055
7045210Chev 75 FEDERAL AT HIGH PERF VETTE72447041459CH2.55103.5406
7045211Chev 75 FEDERAL MT HIGH PERF VETTE72447041459CH2.55103.5406
7045213CHEV & GMC Truck 75-76 Non-CA, HD68327029862CP2.82743.1008
7045216CHEV & GMC Truck, 75-76 Reg Chassis68327029862CP2.82743.1008
7045222Chev 75 AT ALL VETTE72467041459CH2.40963.5406
7045223Chev 75 FEDERAL MT VETTE72467041459CH2.40963.5406
7045228Chev 75 400 FEDERAL AT Chevelle/Monte714717052057DL2.22423.4283
7045229Chev 75 400 MT Truck69367029862DL2.72143.2084
7045504Chev 75 350 AT CALIFORNIA72467037851CH2.40963.5406
7045583CHEV & GMC Truck, 75-77 Calif.73427029862CP2.79993.6545
7045586CHEV & GMC Truck, 75-77 Reg Chassis CA73427029862CP2.79993.6545
17056206CHEV 76 Vette & Nova A/T77487041459CH2.84714.1257
17056207CHEV 76 Vette & Nova M/T77487041459CH2.84714.1257
17056210Chev 76 FEDERAL AT VETTE77517041459CH2.61384.1257
17056211Chev 76 FEDERAL MT VETTE77517041459CH2.61384.1257
17056226Chev 76 FEDERAL AT A/C VETTE77517041459CH2.61384.1257
17056506CHEV 76 Vette & Nova A/T Calif77487041459CH2.84714.1257
17056507CHEV 76 Vette & Nova M/T Calif77487041459CH2.84714.1257
17057203Chev 77 FEDERAL MT NON-A/C VETTE77527041459CH2.53294.1257
17057210Chev 77 HIGH PERF NON-A/C VETTE77537041459CH2.45044.1257
17057211Chev 77 HIGH PERF A/C & NON-A/C VETTE77537041459CH2.45044.1257
17057228Chev 77 FEDERAL A/C VETTE77537041459CH2.45044.1257
17058203CHEV 78 FED VETTE A/C & NON-A/C 4-SPD77527041459CH2.53294.1257
17058210CHEV 78 FED VETTE NON A/C AUTO77537041459CH2.45044.1257
17058211CHEV 78 FED VETTE H.P. A/C & NON 4-SPD77537041459CH2.45044.1257
17058228CHEV 78 FED VETTE H.P. A/C AUTO77537041459CH2.45044.1257
17059203CHEV 79 FED VETTE A/C & NON 4-SPD72407041459CH2.81493.5406
17059210CHEV 79 VETTE L-82 H.P. NON-A/C AUTO77537041459CH2.45044.1257
17059211CHEV 79 VETTE L-82 H.P. A/C & NON 4-SPD77537041459CH2.45044.1257
17059228CHEV 79 VETTE L-82 H.P. A/C AUTO77537041459CH2.45044.1257
17080201CHEV 8071487041459DR2.14963.4283
17080202CHEV 8071427041459CH2.57373.4283
17080204CHEV 8071427041459CH2.57373.4283
17080205CHEV 8072517041459DP2.02873.5406
17080206CHEV 8072517041459DP2.02873.5406
17080207Chev 80 VETTE M/T71427041459CH2.57373.4283
17080212CHEV 807252704145970489921.94783.5406
17080213CHEV 8072507041459DP2.10803.5406
17080215CHEV 8072507041459DP2.10803.5406
17080224CHEV 8072487041459DR2.26193.5406



Figure 2: Metering Areas of Jet & Rod Combinations

JetJet AreaRodRod AreaResulting Area


0.0600.002827430.0260.000530930.0022965
0.0600.002827430.0300.000706860.00212058
0.0600.002827430.0310.000754770.00207267
0.0600.002827430.0320.000804250.00202319
0.0600.002827430.0330.00085530.00197213
0.0600.002827430.0340.000907920.00191951
0.0600.002827430.0350.000962110.00186532
0.0600.002827430.0360.001017880.00180956
0.0600.002827430.0370.001075210.00175222
0.0600.002827430.0380.001134110.00169332
0.0600.002827430.0390.001194590.00163284
0.0600.002827430.0400.001256640.0015708
0.0600.002827430.0410.001320250.00150718
0.0600.002827430.0420.001385440.00144199
0.0600.002827430.0430.00145220.00137523
0.0600.002827430.0440.001520530.0013069
0.0600.002827430.0450.001590430.001237
0.0600.002827430.0460.00166190.00116553
0.0600.002827430.0470.001734940.00109249
0.0600.002827430.0480.001809560.00101788
0.0600.002827430.0490.001885740.00094169
0.0600.002827430.0500.00196350.00086394

0.0610.002922470.0260.000530930.00239154
0.0610.002922470.0300.000706860.00221561
0.0610.002922470.0310.000754770.0021677
0.0610.002922470.0320.000804250.00211822
0.0610.002922470.0330.00085530.00206717
0.0610.002922470.0340.000907920.00201455
0.0610.002922470.0350.000962110.00196035
0.0610.002922470.0360.001017880.00190459
0.0610.002922470.0370.001075210.00184726
0.0610.002922470.0380.001134110.00178835
0.0610.002922470.0390.001194590.00172788
0.0610.002922470.0400.001256640.00166583
0.0610.002922470.0410.001320250.00160221
0.0610.002922470.0420.001385440.00153702
0.0610.002922470.0430.00145220.00147027
0.0610.002922470.0440.001520530.00140194
0.0610.002922470.0450.001590430.00133204
0.0610.002922470.0460.00166190.00126056
0.0610.002922470.0470.001734940.00118752
0.0610.002922470.0480.001809560.00111291
0.0610.002922470.0490.001885740.00103673
0.0610.002922470.0500.00196350.00095897
0
0.0620.003019070.0260.000530930.00248814
0.0620.003019070.0300.000706860.00231221
0.0620.003019070.0310.000754770.0022643
0.0620.003019070.0320.000804250.00221482
0.0620.003019070.0330.00085530.00216377
0.0620.003019070.0340.000907920.00211115
0.0620.003019070.0350.000962110.00205696
0.0620.003019070.0360.001017880.00200119
0.0620.003019070.0370.001075210.00194386
0.0620.003019070.0380.001134110.00188496
0.0620.003019070.0390.001194590.00182448
0.0620.003019070.0400.001256640.00176243
0.0620.003019070.0410.001320250.00169882
0.0620.003019070.0420.001385440.00163363
0.0620.003019070.0430.00145220.00156687
0.0620.003019070.0440.001520530.00149854
0.0620.003019070.0450.001590430.00142864
0.0620.003019070.0460.00166190.00135717
0.0620.003019070.0470.001734940.00128413
0.0620.003019070.0480.001809560.00120951
0.0620.003019070.0490.001885740.00113333
0.0620.003019070.0500.00196350.00105558

0.0630.003117250.0260.000530930.00258632
0.0630.003117250.0300.000706860.00241039
0.0630.003117250.0310.000754770.00236248
0.0630.003117250.0320.000804250.002313
0.0630.003117250.0330.00085530.00226195
0.0630.003117250.0340.000907920.00220933
0.0630.003117250.0350.000962110.00215513
0.0630.003117250.0360.001017880.00209937
0.0630.003117250.0370.001075210.00204204
0.0630.003117250.0380.001134110.00198313
0.0630.003117250.0390.001194590.00192265
0.0630.003117250.0400.001256640.00186061
0.0630.003117250.0410.001320250.00179699
0.0630.003117250.0420.001385440.0017318
0.0630.003117250.0430.00145220.00166504
0.0630.003117250.0440.001520530.00159671
0.0630.003117250.0450.001590430.00152681
0.0630.003117250.0460.00166190.00145534
0.0630.003117250.0470.001734940.0013823
0.0630.003117250.0480.001809560.00130769
0.0630.003117250.0490.001885740.0012315
0.0630.003117250.0500.00196350.00115375

0.0640.003216990.0260.000530930.00268606
0.0640.003216990.0300.000706860.00251013
0.0640.003216990.0310.000754770.00246222
0.0640.003216990.0320.000804250.00241274
0.0640.003216990.0330.00085530.00236169
0.0640.003216990.0340.000907920.00230907
0.0640.003216990.0350.000962110.00225488
0.0640.003216990.0360.001017880.00219911
0.0640.003216990.0370.001075210.00214178
0.0640.003216990.0380.001134110.00208288
0.0640.003216990.0390.001194590.0020224
0.0640.003216990.0400.001256640.00196035
0.0640.003216990.0410.001320250.00189674
0.0640.003216990.0420.001385440.00183155
0.0640.003216990.0430.00145220.00176479
0.0640.003216990.0440.001520530.00169646
0.0640.003216990.0450.001590430.00162656
0.0640.003216990.0460.00166190.00155509
0.0640.003216990.0470.001734940.00148205
0.0640.003216990.0480.001809560.00140743
0.0640.003216990.0490.001885740.00133125
0.0640.003216990.0500.00196350.0012535

0.0650.003318310.0260.000530930.00278738
0.0650.003318310.0300.000706860.00261145
0.0650.003318310.0310.000754770.00256354
0.0650.003318310.0320.000804250.00251406
0.0650.003318310.0330.00085530.00246301
0.0650.003318310.0340.000907920.00241039
0.0650.003318310.0350.000962110.00235619
0.0650.003318310.0360.001017880.00230043
0.0650.003318310.0370.001075210.0022431
0.0650.003318310.0380.001134110.00218419
0.0650.003318310.0390.001194590.00212372
0.0650.003318310.0400.001256640.00206167
0.0650.003318310.0410.001320250.00199805
0.0650.003318310.0420.001385440.00193286
0.0650.003318310.0430.00145220.00186611
0.0650.003318310.0440.001520530.00179778
0.0650.003318310.0450.001590430.00172788
0.0650.003318310.0460.00166190.0016564
0.0650.003318310.0470.001734940.00158336
0.0650.003318310.0480.001809560.00150875
0.0650.003318310.0490.001885740.00143257
0.0650.003318310.0500.00196350.00135481

0.0660.003421190.0260.000530930.00289027
0.0660.003421190.0300.000706860.00271434
0.0660.003421190.0310.000754770.00266643
0.0660.003421190.0320.000804250.00261695
0.0660.003421190.0330.00085530.0025659
0.0660.003421190.0340.000907920.00251327
0.0660.003421190.0350.000962110.00245908
0.0660.003421190.0360.001017880.00240332
0.0660.003421190.0370.001075210.00234598
0.0660.003421190.0380.001134110.00228708
0.0660.003421190.0390.001194590.0022266
0.0660.003421190.0400.001256640.00216456
0.0660.003421190.0410.001320250.00210094
0.0660.003421190.0420.001385440.00203575
0.0660.003421190.0430.00145220.00196899
0.0660.003421190.0440.001520530.00190066
0.0660.003421190.0450.001590430.00183076
0.0660.003421190.0460.00166190.00175929
0.0660.003421190.0470.001734940.00168625
0.0660.003421190.0480.001809560.00161164
0.0660.003421190.0490.001885740.00153545
0.0660.003421190.0500.00196350.0014577

0.0670.003525650.0260.000530930.00299472
0.0670.003525650.0300.000706860.00281879
0.0670.003525650.0310.000754770.00277088
0.0670.003525650.0320.000804250.0027214
0.0670.003525650.0330.00085530.00267035
0.0670.003525650.0340.000907920.00261773
0.0670.003525650.0350.000962110.00256354
0.0670.003525650.0360.001017880.00250778
0.0670.003525650.0370.001075210.00245044
0.0670.003525650.0380.001134110.00239154
0.0670.003525650.0390.001194590.00233106
0.0670.003525650.0400.001256640.00226902
0.0670.003525650.0410.001320250.0022054
0.0670.003525650.0420.001385440.00214021
0.0670.003525650.0430.00145220.00207345
0.0670.003525650.0440.001520530.00200512
0.0670.003525650.0450.001590430.00193522
0.0670.003525650.0460.00166190.00186375
0.0670.003525650.0470.001734940.00179071
0.0670.003525650.0480.001809560.00171609
0.0670.003525650.0490.001885740.00163991
0.0670.003525650.0500.00196350.00156216

0.0680.003631680.0260.000530930.00310075
0.0680.003631680.0300.000706860.00292482
0.0680.003631680.0310.000754770.00287691
0.0680.003631680.0320.000804250.00282743
0.0680.003631680.0330.00085530.00277638
0.0680.003631680.0340.000907920.00272376
0.0680.003631680.0350.000962110.00266957
0.0680.003631680.0360.001017880.00261381
0.0680.003631680.0370.001075210.00255647
0.0680.003631680.0380.001134110.00249757
0.0680.003631680.0390.001194590.00243709
0.0680.003631680.0400.001256640.00237504
0.0680.003631680.0410.001320250.00231143
0.0680.003631680.0420.001385440.00224624
0.0680.003631680.0430.00145220.00217948
0.0680.003631680.0440.001520530.00211115
0.0680.003631680.0450.001590430.00204125
0.0680.003631680.0460.00166190.00196978
0.0680.003631680.0470.001734940.00189674
0.0680.003631680.0480.001809560.00182212
0.0680.003631680.0490.001885740.00174594
0.0680.003631680.0500.00196350.00166819

0.0690.003739280.0260.000530930.00320835
0.0690.003739280.0300.000706860.00303242
0.0690.003739280.0310.000754770.00298451
0.0690.003739280.0320.000804250.00293503
0.0690.003739280.0330.00085530.00288398
0.0690.003739280.0340.000907920.00283136
0.0690.003739280.0350.000962110.00277717
0.0690.003739280.0360.001017880.0027214
0.0690.003739280.0370.001075210.00266407
0.0690.003739280.0380.001134110.00260517
0.0690.003739280.0390.001194590.00254469
0.0690.003739280.0400.001256640.00248264
0.0690.003739280.0410.001320250.00241903
0.0690.003739280.0420.001385440.00235384
0.0690.003739280.0430.00145220.00228708
0.0690.003739280.0440.001520530.00221875
0.0690.003739280.0450.001590430.00214885
0.0690.003739280.0460.00166190.00207738
0.0690.003739280.0470.001734940.00200434
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0.0740.004300840.0260.000530930.00376991
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0.0750.004417860.0260.000530930.00388694
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0.0800.005026550.0500.00196350.00306305



Figure 3: Secondary Metering Rods Listed Rich to Lean


CodeP/NDia of TipTip Length
BV70407240.0300S
CB70423350.0300S
CC70423560.0303M
DC70478160.0303M
BY70408560.0320M
CF70447750.0340M
DG70488900.0340M
AX70335490.0400S
BB70343350.0400S
BF70344000.0400S
BG70348220.0400M
BH70359160.0400M
BJ70360770.0400S
BK70372950.0400S
BM70377440.0400M
BP70380340.0400S
BW70407670.0400M
CA70423040.0400M
CJ70457800.0400S
CM70458400.0400M
CS70459240.0400S
BE70343770.0413S
BL70377330.0413S
BN70366710.0413S
CE70437710.0413L
CY70460040.0443M
DA70460100.0443M
AD70337720.0450S
AH70338120.0530M
AU70336550.0530L
CK70457810.0530L
CV70459840.0530L
BU70407250.0550S
CR70459230.0550S
AJ70336280.0570M
AK70331040.0570S
AL70336800.0570S
AP70339810.0570M
AR70331710.0570S
AV70331820.0570M
AY70338300.0570L
AZ70338890.0570L
BA70343370.0570S
BZ70423000.0570L
CD70427190.0570L
CH70457790.0570S
CN70458410.0570S
CP70458420.0570S
CX70459850.0570L
BD70343650.0580M
BC70343000.0584S
BT70406010.0600M
AT70336580.0670L
CL70457820.0670L
DL70488920.0690S
AN70343200.0700S
BX70407970.0700S
DB70478060.0700S
AS70457780.0777M
CG70457780.0777M
CT70459830.0777M
DE70480920.0877M
BR70389100.0900L
AW70331940.0908M
BS70389110.0950L
CZ70459860.0950L
DD70480910.1050L
DF7048512
DH7048992
DK7048919
DM17050221
DN17053703
DP17053531
DR17053659
DS17056618
DU17059952





Technical Procedure #1:
To pop the top off a Q-Jet, proceed as follows:

1. Remove the air cleaner stud.
2. Using a hammer and a small pin punch or a small finish nail, tap the roll pin holding the accelerator pump lever to the top of the carb in towards the choke horn wall. Don't tap the roll pin all the way up against the wall - leave just a slight gap so you can later get a screwdriver blade in behind it to pry it back again. Remove the accel pump lever.
3. Remove the single screw holding the secondary rod hanger to the top of the carb and remove the hanger with the secondary rods.
4. If you have a later-model Q-Jet with a choke vacuum break diaphragm that is attached to the passsenger side of the carb with two screws up high, remove the two screws and remove the vacuum break and its connecting rod. If your vacuum break is pressed into a bracket that is not attached with 2 screws up high, leave it alone.
5. Remove the choke connecting rod. There are 2 types: One type has a clip holding it to the choke lever. Remove the clip, disengage the rod from the upper lever, then twist/rotate the rod to disengage it from the lower lever inside the carb. Later model carbs have a single screw holding the upper lever to the choke shaft. On this type, remove the screw, remove the lever, and remove the choke rod by twisting/rotating it to release it from the lower lever inside the carb.
6. Remove the (2) 1/2" head bolts at the front of the carb.
7. Remove the 9 top attach screws: Two long screws in the very back; a screw on either side of the secondary airvalves; two screws just forward of the secondary airvalves; two screws just inside the choke air horn right at each primary discharge nozzle, and a single screw center front. If the carb has the stock screws in it, the two screws inside the air horn are designed to be too big to drop down into the intake manifold. But many aftermerket screws can, in fact, drop through the carb and go into the intake. Once you have loosned these two screws, use a pair of needle nosed pliers to carefully lift them out and make sure they don't drop.
8. Lift the top of the carb straight up until it clears the accelerator pump and until the air bleed tubes clear the gasket. If you have a non-removable vacuum break diaphragm, cock the top over to the side to disengage the secondary airvalve rod.
9. Remove the gasket by carefully freeing it from the power piston/primary metering rod hanger.
10. Remove the accelerator pump.
11. Remove the power piston/primary metering rod hanger by pushing it down against its spring pressure and "flicking" it off your fingernail so it pops up. A couple of flicks will disengage the locking collar from the casting, and the assembly can be removed.
12. Remove the phenolic float bowl filler.
13. Remove the float and needle as an assembly.
14. Remove the main jets.

The rods and the jets are stamped with their sizes.

Only trick for re-assembly:

1. When installing the power piston, take care to fish around until the rods drop down into the jets and the power piston works smoothly. Gently push the piston nylon locking collar back into the carb casting. I've seen people not get the rods into the jets, and simply smash the top of the carb down onto the piston/rod assembly. Obviously, this will bend the rods.

Once you have the top back on, installing the choke linkage rod is considered the only "tricky" part. There is a short lever arm down inside the carb, and this arm has a hole in its end. This arm is very easy to see when you have the top off the carb, so I recommend that novices take a look at it and its orientation/function while they have the top off the carb. With the top off, take the choke rod and practice installing/engaging it in this lower lever until you get the knack of rotating the rod slightly to engage it in the hole in the lever.

Once you have the top back on (taking care not to overtighten screws and bolts), activate the choke linkage on the outside of the carb to move this lever arm to its furthest "up" position. You can just barely see it if you look down the carb. Now, insert the choke rod down into the carb, with the rod rotated slightly. Engage the hole in the lever arm at this angle, and once you've hooked the arm, rotate the rod to fully engage it.

Install the accelerator pump lever to the top of the carb. Insert a finish nail or a small pin punch through the roll pin hole to assure that it's aligned, and then use a small screwdriver to pry the roll pin back through the lever.

Install the secondary metering rods with the hanger.

NOTE: If you're going to be doing several jet changes, you do not need to attach the choke linkage rod to run the car. Leave the rod off until you're complete.

Technical Procedure #2
To adjust a Q-Jet with an adjustable Power Piston, proceed as follows:

The Q-Jet uses a power piston with metering rods to lean out the fuel mixture at cruise and at idle, and to richen up the mixture at wide open throttle (WOT). When engine vacuum is high, the power piston is pulled down into the carb against spring pressure, and this inserts the “fat” part of the primary metering rods into the jets for a lean, crisp, economical fuel mixture. When engine vacuum is lost, such as occurs under high power settings, the piston pops up from the spring pressure, and the “skinny” part of the primary rod is all that remains in the jet. This increases the metering area of the jet and richens up the fuel mixture for good power and performance.

Late ‘70s Q-Jets have an externally-accessible adjustment screw (through a small hole in the carb air horn) for adjustment of the power piston height. Many people refer to this as the “mixture screw” on a Q-Jet. Over the years, people have screwed these adjustment screws every way possible in an attempt to “tune” the carbs, and I now frequently see people asking about what the “spec” is for this adjustment. Fact is, there is none. But here’s how you can get your carb set up so it’ll run right again.

You will need to take the air horn (the “top” of the carb) off in order to get this set up properly. See “Technical Procedure #1” this paper for the step-by-step on doing this.

The adjustment screw for the power piston height is located down inside a small bore adjacent to the power piston. You can turn the flat adjustment screw with a pair of needle nosed pliers.

Note that the adjustment screw only adjusts and limits how far DOWN the power piston can go. There is no “up” limit on the piston that is adjustable. In other words, the screw sets the maximum depth that the rods engage into the jets at cruise and at idle. The intent of the adjustment is to assure that the “fat” part of the rod is fully inserted into the metering orifice of the jet under these conditions. If it’s set too shallow, with the skinny power tip portion of the rod in the jet, the mixture will be too rich. If it’s set too deep, the mixture will stay too lean as the engine gets into its power curve. We want to set the height so that the rod is fully inserted in the jet at cruise, but not set too deep.

To do this, you need a pair of calipers. Dial calipers are nice, but I use an old pair of vernier calipers. With the top off the carb, remove the power piston, remove one of the main metering rods, and remove one main metering jet. Lay the jet and the rod side by side on your workbench, and align the rod with the jet such that the top “step” in the rod (the step-up from the fat metering part of the rod to the main shaft of the rod) is aligned next to the bottom of the upper “lip” of the main jet (see Figure bellow) Note that I have given a “range” for this measurement: lining the rod up with the lower edge of the lip is the “max engagement” depth. Lining it up at the mid-point of the lip is the “min engagement” depth. If the rod is in this range, the resultant jetting will be correct. Now, measure the distance from the top surface of the jet to the very top of the rod. Record this number.

Re-install the jet, the rod, and the power piston into the carb. Press down on the power piston until it seats. Using the calipers, measure the distance from the tip top of the main metering rod to the top surface of the jet and adjust the adjustment screw until you obtain the measurement you recorded earlier.

This measurement assures that the rod is fully inserted in the jet at cruise, and this will give you correct, excellent performance.

Answer 2

This Site Might Help You.

RE:
I need help tuning my quadrajet!?!?!?!?
Does anyone REALLY know how to tune a quadrajet? I need help!?
I just had a 383 stroker built for my 68 chevelle malibu. I put an edelbrock torquer manifold on it but dont have the money yet for a new carburator. But I already have a near new Rochester Quadrajet rebuilt by Holley. I would like to...

Answer 3

The quadrajet was a good card, just bad mouthed by all the Holley fans.
They are simple and basically fool proof.
The primary and secondary both run fixed jets with metering rods. the rear rods work off a cam in the upper butterfly that raises them when vacuum opens the secondary upper butterfly.
The secondary is controlled by both spring pressure that is adjustable on the upper flys and by the vacuum break that hooks to the secondary linkage. You really shouldn't have to mess with these if they are working. Apply vacuum to the break and be sure that it pulls in and holds. Be sure that the upper flys snap shut when you push them open by hand with the engine off.
the primary metering rods are adjustable. There is a screw between the two idle adjsuting screws in the lower plate. usually it is covered with a drive in plug that will have to be popped out. it will be either a plain screw driver head or a double "D" depending on the year. Screwing this in raises the lean stop of the mixture and allows a faster enrichment under accel.
If that still isn't getting you enough fuel you can change the jets, going up 2 thousands on each side at a time.
On the acclerator pump lever use the outside hole for the rod. This will raise the plunger a little higher giving you a better blast of gas on accel.
With a gas analyzer you can look for a 14.7 fuel mix at cruise, but you probably don't have one of those handy.
Drive the crap out of it, pull a plug on each bank and look at them. They should be turning a light brown. If they are turning black you have too much fuel.
Most of the Hot Rod carb problems I see are from too much fuel, not too little.
One of the most overlooked problems on these is the "well plugs" that cap the cross drilled passages in the fuel body. They are set in with a lead filling. There is a repair kit for them but you can just reseat them with a ball pen hammer tapping lightly on the lead seal.
Good luck

Answer 4

Quadrajet Power Piston

Answer 5

Contact Tim B for a rejet/reset To get it in the ballpark close up both screws for the enrichment and back out 1 and 1/4 turn It will start up on this. Myself,I would have bought the one for a 396/375 big block

Answer 6

Any time I've adjusted a carb, I used a exhaust gas analyzer to make it perfect. Adjusting by ear doesn't work well at all. It would be best to save up some cash and take it to a performance place and let them do it.

Answer 7

Natural Penis Enlargement Guide : http://LongPenis.uzaev.com/?qCFf

Answer 8

Contact Holley for the correct procedure or, Purchase a new 3-barrel carb. 383 is a sweet engine.

Answer 9

get a vaccumn gauge and start turning the adjusting screws -you want the highest vaccumn reading you can get --and as far as a couple said get a holley if you really wanna work on carbs go ahead get a holley--make sure gauge is hooked to a vacumn port

Answer 10

the rochester should have 2 adjusting screws for air/fuel mix @ the base of the carb. set idle @ apprx 1000 rpm (a tach helps) then back off the left screw (counter clockwise) until the engine starts to die, then dial it back appprx 1 and a quater turns until smooth idle/max rpms returns. repeat the process on the right screw. should give you a pretty good air/fuel mix. back the idle down to desired rpm apprx 500-600 and take it for a spin.

Answer 11

Junk it and buy a Holley