Tuning The Burn -- Edelbrock Carburetors -- Super Chevy

Edelbrock's AVS Carbs Are Street Worthy

Mike Petralia Feb 28, 2006 0 Comment(s)

That myth goes way back, almost to the beginning of high performance. The carburetor has been the Pandora's box of performance bolt-ons. They've never been thought of as easy to tune or fun to run. They leaked, they ran inconsistently, and it almost took a Master's degree in fuel system engineering to figure one out. But not anymore. Edelbrock's newest entrant into the fuel-mixing arena has addressed many of the problems that plagued carburetors of old. And just because our cars are getting older, that doesn't mean our carbs have to be.

NO LEAKS BELOW
We hate leaks (especially dangerous and unsightly fuel leaks coming from a part that sits right on top of a hot engine)! Edelbrock's Thunder Series AVS carburetors have basically just one gasket that's above the fuel level so fuel won't seep out of it over time and cause ugly stains on our intake manifolds. And making any type of fuel curve adjustments or idle adjustments on the AVS carbs won't cause any spilled fuel either. Though it's not necessarily safe or smart to do so, you could actually change the fuel curve with the engine running, since the metering rods can be removed from the top of the carb without spilling a drop of gas.

ADJUSTABLE TUNING
The secondary circuit of a four-barrel carburetor is what can really make the power. When those two extra butterflies open, adding tons of fuel and air to a thirsty engine, a four-barrel carb really roars to life. But tuning four-barrels has been tricky, until now. Most street engines with automatic transmissions behind them don't work that well with big mechanical secondary carbs, (i.e. 750-plus-cfm carbs that have secondary butterflies mechanically linked to the primaries so they open whenever your foot is more than about halfway down on the floor), so we've always recommended running vacuum secondary carbs on the street. Ironically, vacuum secondary carbs don't always produce the best power figures on the dyno, due to the relatively short time we spend at WOT, and so we almost always use mechanical secondary carbs when testing. It gets confusing, we know, but trust us when we tell you that your daily driver will run much better using a vacuum secondary carb.

Thankfully, Edelbrock has taken the guesswork and tuning troubles out of the secondary side of its new carbs by designing an adjustable valve secondary (AVS), which allows you to change the vacuum secondary's opening rate with a quick turn of a screw. Even though the secondary air door is spring loaded, there are no springs to change here. Just loosen one Torqx-head locking screw and turn the adjustment screw to speed up or slow down the secondary's opening rate. It's that easy. The AVS carbs also feature two-step metering rods for independent tuning of the cruise and power circuits.

SIZE MATTERS
Of course, like most other performance carbs on the market today, the AVS comes in different sizes. But there are only two sizes to choose from, so the choice is simple. The 650-cfm AVS carbs can handle about 90-percent of cars on the road/track today. If your car has more than 400-cid, or you plan to ring out your 355 on some high-rpm power runs on a daily basis, then the 800-cfm AVS carb should cover you. And both of these carbs come with either a manual choke, for those of you who like choking your rod every morning, or an electric choke version for the rest of the civilized world. All told, there's only four part numbers to choose from, making carb selection that much easier.

OTHER FEATURES
The AVS line of carbs also has some nice plumbing features like the dual-inlet fuel option that comes on every carb. That means that you're able to pump fuel into either side of the carb to make routing and hiding your fuel lines that much easier. Or you can route fuel to both sides of the carb using Edelbrock's dual feed fuel line kit that's available in either the traditional blue/red anodized aluminum finish (PN 8133) or in fully-polished finish (PN 8128). And the dual feed fuel line also includes its own fuel filter as an added bonus.Any way you slice it, there's no need to fear carburetors any longer. Edelbrock's AVS carbs make swapping and tuning them almost as easy as filling up with gas. And their bright aluminum finish means they're not so bad in the looks department also, which is something we all strive to be.

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Edelbrock's ingenious adjustable valve secondary (AVS) technology gives users the ability to change secondary opening rates with a simple turn of this screw. That gives you better drivability and smooth transition from cruise to wide-open throttle.

Notice how the screwdriver hangs firm on the idle speed adjustment screw, which means it won't slip off when you're trying to make adjustments on a running engine.

The screwdriver locks firmly into the Torqx-socket of the idle mixture adjusting screws. You can also use a regular flat-blade screwdriver on all of the idle adjustment screws.

Adjusting the electric choke on the AVS carbs is easy. Edelbrock has taken the extra step of highlighting the adjustment marks on the choke housing for us.

Here's really the only parts you may someday have to swap in order to tune your fuel curve. The two-step metering rods control fuel flow into the engine and can be pulled out by loosening just one screw. Edelbrock includes jets and rods for calibration with each new carb. A tuning kit (PN 1480) is also available for more in-depth adjustments.

The 650-cfm AVS carbs (left) are a classic spread-bore design, meaning that the primary venturi is smaller than the secondary venturi. This gives you good cruising and better economy than the 800-cfm AVS carb with its equal-sized venturi square-bore design.

Here's an AVS carb in all its glory. After pulling the metering rods, there are only 8 screws to remove and two rods to disconnect and the entire top half of the carb comes off. The fuel level stays in the bottom "main well" of the carb, below the gasket line to avoid leaks.

Edelbrock offers a complete tuning kit for making fine adjustments to the AVS carbs.

A tuning guide is included with AVS carb to take the guesswork out of making adjustments.

This is about all you'll need to tune an Edelbrock AVS carb. Not too many tools to have to haul around with you just in case.

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