Answered by Edelbrock, Holly and Demon

Good read

http://www.hotrod.com/articles/ccrp-...ions-answered/


We polled the experts at Holley, Demon and Edelbrock for responses to our most probing induction queries.

Factory production vehicles haven’t rolled off the Big Three’s assembly line with new carburetors since the ’80s, but it’s still the most popular choice of induction among car crafters. Don’t get us wrong; we understand that the latest and greatest computerized fuel-injection systems are getting more affordable and enable today’s performance tuners to tame mega-horsepower engines for docile street use, but no matter how you look at it, carburetors will always be cheap and effective if you know how to properly tune them. But carb experts–the guys who spend all day on the phones with real-world users–tell us it never ceases to amaze them how many people are completely lost when it comes to understanding the nitty-gritty details of how a carb really works and how to tune one for maximum performance.

Over the years we’ve shown our readers everything from how to rebuild carburetors to how to live with one every day. This time we’re going step further by directly probing minds from Holley Performance, Demon Carburetion, and Edelbrock for answers to 20 of the most common carburetion questions from basic to advanced. Even you expert carb gurus out there might learn something new.

Q: Does a bigger carb make more power? What’s the limit?

Demon Carbs responds: Larger carburetors can make more power on a dynamometer, but this can also result in slower acceleration and lower efficiency of fuel atomization. Generally we find that you’re better off leaning towards a slightly smaller carburetor than a larger one, as it’ll operate more efficiently and provide better acceleration for the vehicle.

Q: Where should I hook up my vacuum advance?

Edelbrock responds: If you’re unsure of which port to use, connect the vacuum line to the timed vacuum port. This has no vacuum at idle and won’t affect idle quality. However, if your application requires vacuum at idle, you’ll want to connect the line toe manifold vacuum port. The most detrimental effects of using the wrong port is an increase or decrease of rpm and poor idle characteristics. Generally the distributor vacuum line goes to the timed port.

Q: What’s the best way to tune the accelerator-pump circuit?

Holley Performance responds: The accelerator-pump system consists of three main components: the pump diaphragm, the pumpkin, and the pump nozzle. This is the carburetor system that is most responsible for having good, crisp, off-idle throttle response. Its purpose is to inject a certain amount of fuel down the throttle bores when the throttle is opened to smooth the transition between the idle and main circuits so that no stumble, hesitation, or sluggishness will be evident during this transition phase.

The first adjustment to check is the clearance between the pump operating lever and the pump diaphragm cover’s arm, at wide-open throttle. This clearance should be around 0.015 inch. This ensures that the pump diaphragm is never stretched to its maximum limit at wide-open throttle, which will cause premature pump failure. Next, make sure the accelerator-pump arm is activated the moment that the throttle begins to move, which ensures instantaneous pump response. These adjustments can be made by simply turning the accelerator-pump adjusting screw located on the accelerator-pump arm together with the pump override spring and locknut.

The amount of fuel delivered by one accelerator-pump stroke is determined by the pump’s capacity and the profile of the pump cam. The time it takes for that fuel to be delivered is controlled by the pump-nozzle size. A larger pump nozzle delivers the fuel much sooner than a smaller pump nozzle. During acceleration tests, if you notice that the car first hesitates and then picks up, it’s a sure bet the pump-nozzle size should be increased. A backfire (lean condition) on acceleration also calls for a larger pump-nozzle size. Conversely, if off-idle acceleration does not feel crisp or clean, the pump-nozzle size may need to be decreased. Holley accelerator-pump nozzles are stamped with a number that indicates the drilled pump hole size. For example, a pump nozzle stamped “35” has a 0.035-inch orifice. Pump nozzle sizes are available from 0.025 to 0.052 inch. Whenever a 0.040-inch or larger accelerator-pump nozzle is installed, the “hollow” pump-nozzle screw (PN26-12) should also be used. This screw allows extra fuel to flow to the pump nozzle, assuring that the pump nozzle itself will be the limiting restriction in the accelerator-pump fuel-supply system.

When changing the pump nozzle, it’s best to jump three sizes. For example, if there’s an offline hesitation with a No. 28 pump nozzle, tray No. 31 pump nozzle. If you must use a No. 37 (0.037-inch) or larger pump nozzle, then also use a 50cc pump. A 50cc accelerator-pump conversion kit is available under Holley PN 20-11 when maximum pump capacity is desired.

Once nozzle size has been selected, the accelerator-pump system can be further tailored with the pump cam. Holley offers an assortment of different pump cams, each with uniquely different lift and duration profiles that are available under Holley PN 20-12. The cam profile affects the movement of the accelerator-pump lever and, subsequently, the amount of fuel delivered by the pump nozzle.

Installing a pump cam is a simple matter of loosening one screw, placing the new pump cam next to the throttle lever, and tightening it up. There are two or three numbered holes in each pump cam. Placing the screw imposition number 1 activates the accelerator pump a little early, allowing full use of the pump’s capacity. Generally, vehicles that normally run at lower idle speeds (600 or 700 rpm) find this position more useful because they can have a good pump shot available coming right off this relatively low idle. Positions number 2 or 3 delay the pump action, relatively speaking. These two cam positions are good for engines that idle at 1,000 rpm or above. Repositioning the cam compensates for the extra throttle rotation required to maintain the relatively higher idle setting. Pump-arm adjustment and clearance should be checked and verified each and every time the pump cam or pump-composition is changed.

 

Q: How do I choose the right size carburetor for my engine?

Edelbrock responds: A simple formula can assist you with this. Multiply your cubic-inch displacement by the maximum rpm limit and then divide by 3,456 to represent the volumetric efficiency. The result is the amount of cfm the engine requires at the maximum rpm limit.

Example:
350 ci x 6,000 rpm = 2,100,000
2,100,000 / 3,456 = 608cfm
A 600-cfm carb would be sufficient.

Q: Is air pushed or sucked into a carburetor?

Demon Carbs responds: Unless you are working with a forced-induction system (centrifugal supercharger or a turbocharger system) that forces air through the carburetor, air is pulled through the carburetor based on the engine’s vacuum signal.

Q: Where should the fuel-pressure regulator be located and what type should I use?

Demon Carbs responds: The pressure regulator should be mounted as close as possible to whatever you’re feeding (e.g. Carburetor, nitrous system). The farther away the regulator is, the longer it will take to open and close in response to demand, which can cause spikes in fuel pressure. The type of fuel pump you’re using along with the fuel requirements of the engine will be the determining factors for the type of regulator you’ll use.

Q: How does a metering rod work and how do I tune with one?

Edelbrock responds: Fuel must pass through the restriction created by the main jet and metering rod before entering the engine. The rod extends through the jet, reducing the amount of area for fuel flow. Similar to power valves, metering rods add fuel when ascertain engine load or vacuum drop is reached. The two metering rods in an Edelbrock carb have stepped ends that protrude into the main jets and restrict or increase the flow of fuel through the orifice proportional to engine load. If the diameter of the rod is large, then fuel flow through the jets is more restricted than if the rod were small. Specially tuned springs are used to adjust the vacuum levels required to actuate the rods under various load conditions. There is nipper-determined” combination of rods and jets for any given engine. Each engine may require a different fuel curve. The best thing to do is run the carburetor on the engine right out of the box, then check the sparkplugs and see how they look. You need to have a golden brown color on the plugs. If they are too white or too black, you need to make adjustments.

Q: How do I know what size power valve to use?

Holley Performance responds: The power-enrichment system supplies additional fuel to the main system during heavy-load or full-power situations. Holley-style carburetors utilize vacuum-operated power-enrichment system and a selection of power valves is available to “time” this system’s operation to your specific needs.

Each Holley power valve is stamped with a number designating the vacuum opening point. For example, a “65” indicates that the power valve will open when engine vacuum drops to 6.5 in-Hg or lower. An accurate vacuum gauge should be used when determining the correct power valve to use.

A competition or race engine with a long-duration high-overlap camshaft will have low manifold vacuum at idle speeds. If the vehicle has a manual transmission, take the vacuum reading with the engine warmed up and at idle. If the vehicle is equipped with an automatic transmission, take the vacuum reading with the engine warmed up and idling in gear. In either case, the power valve selected should have a vacuum opening point about 2 in-Hg below the intake-manifold-vacuum reading taken.

A stock engine, or one that is only mildly built for street use, will have high manifold vacuum at idle speeds. To determine the correct power valve, drive the vehicle at various steady speeds and take vacuum readings. The power valve selected should have an opening point about 2in-Hg below the lowest steady-speed engine vacuum observed.

Most popular Holley performance carburetors incorporate a power-valve-blow-out protection system. A special check valve is located in the throttle body expressly for this purpose. This check valve is designed to be normally open but will quickly seat to close off the internal vacuum passage when a backfire occurs. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve.

Q: How much clearance should I have from the top of the venture to the lid of the air filter?

Edelbrock responds: A minimum of 3/4 to 1 inch is recommended for proper airflow.

Q: How do an air door, an air-valve secondary, and vacuum secondaries differ?

Edelbrock responds: An air door is typically a counter weighted set of throttle blades that operate separately from the actual throttle blades of the carburetor but is located inside the carburetor body. It is only accessible by removing the top of the carburetor and is not easily adjustable. The purpose of an air door is to allow a smooth transition from the primary circuit into the secondary circuit. Rather than giving 100 percent of the secondary’s “flow” all atone to the engine, the counterweighted air door opens gradually as the draw from the engine increases with rpm, therefore slowly allowing more air and fuel into the engine.

An air valve operates pretty much the same way as an air door, but it is not located inside the carb, and it is adjustable. This is a spring-loaded air valve, or “flap” that sits in the top portion of their horn of the carburetor, and you can adjust the amount of tension on the valve by means of a screw. Making the tension tighter brings the secondary’s full potential in later in the rpm range, and loosening the tension brings it in earlier.

Vacuum secondaries typically only apply to Holley-style carburetors. This is a diaphragm with a spring inside that sits off to the side of the carburetor but is still part of the carburetor and operates the secondary’s using the engine’s manifold vacuum. It is adjustable by means of a spring that can be removed and replaced inside the diaphragm.

Q: Why is it necessary for a blower carb to be boost referenced?

Holley Performance responds: A carburetor does not sense the vacuum of the engine when there is a supercharger between the carb and engine. This lack of vacuum causes the power valve to remain open. Referencing the power valve to the lower intake allows the power valve to operate properly, giving precise fuel metering as you would achieve without the supercharger. If the power valve is not referenced to the lower intake, it can be sucked shut from the high vacuum signal from the blower. This will cause the engine to run 6 to 8 jet sizes too lean, possibly causing engine damage.

 

Q: How is jet size determined and why do two jets with the same hole sometimes flow differently? Can I just drill jets to a bigger size?

Holley Performance responds: There is a basic misconception that size alone determines jet flow characteristics. This is not the case because the shape of the jet entry and exit, as well as the finish, affects flow. Holley jets are finished-drilled in an environmentally controlled room so tolerances are as close as possible each time a set of jets are run. Holley takes into consideration the jet entry, exit, and finish as a constant variable. Samples are taken at various times during each jet run to be sure the machines are holding tolerances and flow. These hole sizes are measured in thousandths and the jet part number generally matches the hole size–give or take one thousandth–on jet sizes up to 70. For example, a PN 122-44 jet has a hole size of 0.044 inch. Above a 70 jet, the hole sizes are significantly larger than the number.

Holley has allowable tolerances for each standard jet size, which explains why some jets with the same number can seem to flow differently. For example, the tolerance range on a 65 jet ranges from351.5 to 362 cc per minute while a 66 ranges from 368.5 to 379.5 cc’s. Those tolerance ranges explain why a 66 jet may not always give a richer mixture than a 65–if the 65 is on the “high” side of the tolerance and the 66 is on the “low” side. The two jets may flow very close to the same.

Holley offers close-limit jets that range in size from 60 to 74. The jet numbering follows that of a standard jet with a third number added. For example, a jet stamped with PN 122-632 indicates it is a 63 jet. The third number, 2, is added to indicate whether the jet flows on the lean side (631), the middle (632), or the rich side (633) of the flow band. There is about a 1.5 percent difference in flow between each of the three jets in a flow band, for a flow range difference of 4.5 percent. Holley close-limit jets are only offered in the middle flow range.

Drilling out jets is never recommended because this always alters the entry and exit features to some degree and may introduce a swirl pattern even if the jet is held in a pin vise and carefully drilled. You cannot be sure of the flow characteristics of a jet that you modify by drilling–unless you can get that jet back on a flow machine to compare it with a standard jet.

Q: How do you tune a vacuum-operated secondary?

Holley Performance responds: Carburetors with vacuum-operated secondary’s are popular for street vehicles because they are very forgiving, and correct carburetor size selection is not as critical as with mechanical-secondary carburetors. The vacuum secondary’s only allow the carburetor to flow the necessary air and fuel based on the engine’s demand. Vacuum for the diaphragm is obtained from the primary venturis with some being bled off through an opening into one of the secondary’s. As engine rpm goes up, velocity through theprimaries creates a vacuum signal. The amount of secondary opening is initially dependent on airflow in the primaries but is later augmented by the vacuum in the secondary barrel through the previously mentioned bleed opening. If a carburetor is too large for an engine, the vacuum diaphragm “sizes” the carburetor so it flows only the necessary amount by partially opening the secondary’s.

Tuning the vacuum secondary’s is very simple. Holley offers color-coded springs of various tensions. This enables the engine’s vacuum to pull open the secondary’s either sooner or later depending on the spring tension. White springs are the lightest and allow the secondary’s to open sooner, while black Holley springs delay secondary opening the longest and open them at the slowest rate. Holley spring kit PN 20-13includes seven springs for proper tuning.

Q: How do you set the float level and what effect does it have?

Demon Carbs responds: For street-driven Demon carburetor applications, we recommend starting with the float level 1/4up the sight window. Changing the float level changes the amount of fueling the bowl (reservoir) to feed to carburetor jets. Raising the float level can help the engine respond quicker if you’re having a lean stumble, while lowering the float level can delay the start of the main metering circuit, in effect helping lean the mixture coming off idle.

Q: We’ve seen some carburetors with drilled throttle butterflies. Why and when is it necessary?

Holley Performance responds: Yes, some Holley carbs do come with drilled butterflies. Typically these are found on our HP-series carbs. This was a performance feature that we added because these carburetors are mostly purchased for high-performance race engines that require extra air when the butterflies are closed to idle properly. Sometimes drilling the butterflies is required on carburetors for engines utilizing a cam with a narrow lobe separation, which in turn creates low manifold vacuum. The large cam requires more air and fuel to idle. Most people open the curb idle screw so much that the butterflies open far enough to expose the main circuits, causing engine rpm to jumps high that turning the idle-mixture screws have no effect on engine rpm. Usually this condition can be corrected by closing the curb idle screw down to just below the idle transfer circuit slot and opening up the secondary throttle blades with the secondary-throttle-blade screw. Many people are not aware that there is a secondary-throttle-opening screw. In rare occasions, drilling the butterflies would still be required if opening up both sets of throttle blades did not provide enough air for the engine.

Q: When should I use a double-pumper instead of vacuum-secondary carb?

Demon Carbs responds: Generally you should use a mechanical-secondary carburetor on vehicles equipped with manual transmissions or with an automatic transmission using a 3 ,000-rpm-or-higher stall converter. On automatic-transmission-equipped vehicles with less than 3,000-stall converters, the vacuum-secondary carburetor is the best choice because the design of the double-pumper can dump so much extra fuel into the engine that a rich bog may occur.

Q: How do you diagnose the cause of a bog or stumble?

Edelbrock responds: There are different kinds of “bogs “and “stumbles”; each situation has a different meaning to different people, and a different feel as well. You can have a lean bog or a rich bog; you can have the same with a stumble. Keep in mind that a bog and a stumble are pretty much the same thing. If the vehicle tends to fall on its face–step on the throttle and the engine just wants to die–typically this is a rich bog. If too much fuel enters the engine too soon and the engine can’t handle it, it makes no power and doesn’t want to go anywhere. A lean bog or stumble would give more of a jerky motion and tend to “pop” back through the carburetor. No matter what situation you encounter, you will need to check the basics first, including fuel pressure, float level, ignition timing, and spark plug color to determine which direction to go for the cure.

Q: What’s the difference between a straight-leg booster, a down-leg booster, and an annular-discharge booster? Does booster design affect jetting?

Demon Carbs responds: The straight-leg booster has, as the name implies, a straight leg out from the main body with a discharge ring above the carburetor’s venturi. A down-leg or drop-leg booster drops the discharge ring lower into the venturi where it is in the higher velocity airstream, which will pull more fuel than a straight-leg-style booster. An annular-discharge booster has a larger ring with multiple discharge holes rather than the single outlet hole of a straight-leg or down-leg-style booster. This creates a venturi inside the main venturi that will create more vacuum signal to pull even more fuel. There are several pros and cons for each type of booster based on the application they are installed on. If you were to run each style of booster in the same carburetor with all else being equal, the down-leg booster would require a smaller jet to flow the same amount of fuel than would a straight-leg booster, while the annular-discharge booster requires an even smaller jet to flow the same amount of fuel as the down-leg booster.

Q: How does weather and altitude affect carb jetting?

Demon Carbs responds: Put very simply, the more oxygen there is in the air, the more fuel–and therefore, the larger the jet size–the engine needs. As the temperature gets colder or the altitude gets lower, there is more oxygen in the air, so you’ll need to go up on the jet size to add more fuel. Conversely, as it gets warmer or you go higher in altitude, you’ll need to go down on your main jet size.

Q: How do I know what size and type of needle-and-seat to use?

Holley Performance responds: Holley offers a variety of needle-and-seat assemblies for its carburetors. The configuration of the needle-and-seat assembly and its seat size depend on carburetor application, cfm rating, and type of fuel bowl used.

Seat size determines the maximum amount of fuel that can flow through it at a given pressure. A bigger seat flows more fuel. Most Holley performance carburetors come with Viton-tipped needles. The Viton needle design is resistant to dirt and conforms nicely to the shape of the seat for superior sealing. For this reason it is not recommended to use a steel or titanium needle, except for racing. In street and mild race applications, a 0.110-inch Viton assembly (PN 6-504) is standard and flows sufficient fuel for carbs up to 850 cfm. Viton PN 6-518-2 has seat size of 0.120 inch and is standard on carburetors like Holley’s 950and 1,000 HP as well as Dominators.

Holley offers steel-tipped inlet needles that are necessary when using exotic racing fuels or alcohol, or when using benzene or acetone additives. A 0.097-inch steel seat size should be used for small four-barrel carburetors; a 0.110-inch steel seat size should be used for carburetors up to 735 cfm; larger seat sizes should be used with carburetors 750 cfm and larger.

Holley also offers a titanium inlet needle with a 0.150-inch seat. This is about as big as you can get. Its design is very responsive to changes in flow rates and has excellent sealing capabilities.

 

....

 

Good read for all those who are either having issues with their Holleys or are thinking about making the transition (*cough* downgrade *cough*) to a holley.

I reckon this could be worth someone making it a sticky.

 

This is probably the most important one in there for us

Q: Does a bigger carb make more power? What’s thelimit?

Demon Carbs responds: Larger carburetors can make morepower on a dynamometer, but this can also result in slower accelerationand lower efficiency of fuel atomization. Generally we find that you’rebetter off leaning towards a slightly smaller carburetor than a largerone, as it’ll operate more efficiently and provide better acceleration for the vehicle.

 

I would respectfully disagree with several of those, and would want to expand on some others.

That's only the BEGINNING of determining carb size. Although, I like their choice of words about "simple" and "can assist", instead of claiming "complete" and "predicts" or some such. It's just the beginning of the selection process, not the end. Ideal carb size is also strongly affected by the degree to which the air flow is constant vs pulsating. A dual-plane intake causes 4 cyls to draw through one half of the carb, and the other 4 through the other half. During the periods of time in between each cyl's pulse of air, NO air is flowing through the carb; but DURING the pulse, a MUCH higher volume could be flowing; e.g. for the 350 spoken of above, there might be 900 CFM flowing DURING ACTUAL FLOW EVENTS, and not 600 smoothly at all times. Most of the time we have no idea how much air we actually need to accommodate during those peaks of flow. This effect is further amplified by a small plenum (a large plenum smooths out the time rate of flow), the runner volume, and so on. A single-plane intake with a large plenum comes closest to being predicted by this formula, MUCH closer than a typical street setup. This whole effect is why the factory successfully used a 3310 (780 CFM) on 327s in the 60s, which also came with a dual-plane intake with a VERY small plenum; the above "formula" would predict a 550 CFM carb or some such. In reality, for maximum power especially in most street design engines, the optimum carb size will generally be larger than this "formula" predicts.

However, most people also grossly overestimate the need for totally unrestricted air flow at WOT, at the expense of compromising good performance at lower flow rates. Even if an engine makes better numbers on the dyno at max power and max RPM, it might still be faster and peppier and more efficient and otherwise more pleasant to drive on the street if "get me the biggest possible number for chicken-choking purposes" wasn't the sole criterion for optimization.

Air is ALWAYS "pushed" through the carb. It is impossible to "pull" air without something like a parachute. (duh) The ACTUAL answer should be, the air is PUSHED through the carb, by atmospheric pressure: as the pistons descend into the bores, the air in the intake system "attempts" (I use quotes because there's no will or purpose involved, just thermodynamics) to expand to fill the space, lowering the pressure in the intake (aka "manifold vacuum"); then atmospheric pressure PUSHES air back into it to "attempt" to restore equilibrium. Therefore the MAXIMUM POSSIBLE pressure forcing air into the engine, is atmospheric, under whatever conditions; 14.7ish psi @ sea level etc., and usually somewhat less than that.

This description of Holley vacuum secondaries, coming from Holley's competitor, is amusing. It is WRONG!! The vac sec diaphragm IS NOT operated by manifold vacuum!!!! If it was, its discipline would be EXACTLY BACKWARDS to what is desired: it would RELAX at WOT, instead of OPERATING. In reality, this is operated by VENTURI vacuum, NOT manifold vacuum; which is, the same signal that causes fuel to be fed through the main system. As the air velocity through the primary venturi increases, its pressure decreases, creating "vacuum" of a sort. A sample of that is then used to operate the sec diaphragm. In effect, the sec throttles are opened just to a point at which there is no longer enough flow through the pri venturis to sustain their opening any further, and the whole thing thus reaches an equilibrium where the sec throttles open only just enough to maintain a roughly constant flow through the pri bores.

While the article is very thorough and correct as far as what it says, it's MISSING some EXTREMELY IMPORTANT details. Most notably, that the fuel flow through the main system (jets) is determined by 4 things: engine demand, the relation between air flow and venturi vacuum, air bleed size, and jet size. Engine demand is how much air the engine consumes at each given power level; so for example, a LARGER engine typically requires SMALLER jets if all else is equal, because a SMALL engine at max power RPM will demand the same amount of air as a LARGER engine at some lesser throttle opening, and in fact the difference could be SO GREAT as to correspond to WOT in the SMALL engine (needing high fuel flow at that air flow volume) but CRUISE in the LARGER engine (and therefore not needing near as much, or potentially even ZERO, power enrichment).

One could add a 5th element to this, that being, the fuel bowl level; which determines among other things how much venturi vacuum (after being bled off by the air bleeds) is required to raise the fuel up to the level of the discharge, i.e. the amount of air flow into the engine at which ANY fuel flow through the main system begins to occur AT ALL. Below that flow, ALL fuel is fed through the idle system; and even once the main begins to flow, the idle circuit continues to be a significant contributor up to a surprisingly high air flow (power) level.

The air bleed size point is CRITICAL to understanding why the classic message board post "what size jets should I use" is so misguided. If 2 people have carbs with 2 different air bleed sizes, as is typical of different carb models, their jet size requirements EVEN FOR THE SAME ENGINE will end up being VASTLY DIFFERENT, even if all else is equal. It is ridiculous to expect that just because "all the fast cars", or even "YOUR fast car", use size xx jets, then size xx MUST be the right one for MY car, unless FAR more details are known.

In the later Q they talk about the types of boosters and discharges, which adds further variables into the relationship between jet size and fuel flow, partly by affecting the strength of the venturi vacuum signal. One Internet poster who has a straight-leg booster is going to need a VASTLY different jet size than some other Internet poster with annular-discharge ones, ceteris paribus.

I also notice that Holley's instructions for selecting a power valve are MUCH better here than in all of their publications for all these years. Specifically, the "half of engine vacuum" mistake myth they've been feeding us for as long as I've been in this hobby. 2" below idle vac is a pretty good rule-of-thumb starting point, once the jets have been properly sized. It may not be "right" let alone "perfect" or "ideal", but it's a good start in that it should at least be in the right area code, or maybe even ballpark, and run well enough to allow fine-tuning from there. The jets by themselves should be sized to supply fuel correctly at low-load conditions, then the power system should IMMEDIATELY begin to enrich the mixture as load increases. (in a Holley... not all carbs work like this, notably Q-Jets) Once the jets have been sized for correct mixture at cruise, then the power system should begin operating almost as soon as the throttle is opened further, rather than requiring the throttles to open a YUUUUUJJJJJE amount before enrichment occurs, which is what causes that llllloooooooonnnnnnngggg flat spot or "Holley stumble" that inevitably occurs if you fall for that "half of idle vacuum" eff-up.

Other than that, a very good read.