Q&A

Ask Away! with Jeff Smith: Adjustments for an Edelbrock AVS2 Carburetor with a Slight Hesitation

I recently bought one of those new 750 cfm Edelbrock AVS2 carburetors for my 1969 Satellite with a 383 V8. It runs pretty good but it has a slight hesitation when I nail the throttle hard at low speeds. I’m just learning about carburetors but I don’t see any accelerator pump like on a Holley. Is there a way to adjust the carburetor so that it will not bog when I hit the throttle hard?

S.T.

This is the Edelbrock AVS2 carburetor. The AVS2 refers to the upgraded annual boosters that make this a great street carburetor. (Image/Jeff Smith)

The Edelbrock AVS2 carb was a great choice for your 383.

The AVS name is an acronym that stands for Air Valve Secondary. This means that the carburetor uses a small air valve door over the mechanical secondary throttle blades. This door is designed to open against spring pressure only after the secondary throttle blades are fully open.

As you mentioned, mechanical secondary Holley carbs use an accelerator pump nozzle to squirt fuel into the secondaries to compensate for a lean air-fuel ratio mixture when the throttle blades are opened quickly—especially at low engine speeds.

The Edelbrock carburetor does not use these squirters, as you noticed. The idea behind the air valve door is to gradually open to create enough air velocity past the secondary boosters to create a sufficient signal to begin to pull fuel from the boosters into the engine.

The air valve door is spring-loaded directly on the shaft and it is adjustable. If you are experiencing a hesitation or a bog, this likely means the air valve door is opening too quickly and not creating enough velocity to initiate the boosters, so the engine experiences a lean hesitation.

The fix is extremely easy.

The photos at the bottom of this article will show you the location of a small Torx brass locking screw that holds down a slot in the shaft. A large flat-bladed screwdriver will adjust the spring tension once the lock screw is loosened. In your case, loosen the Torx locking screw and slightly tighten the spring tension by about 1/8-turn. This should create sufficient tension to slow down the opening just enough to create the proper velocity to trigger the boosters sooner, which will then eliminate the hesitation.

Understanding Hesitation & Carb Calibration

Some people interpret a slight hesitation when the secondaries slam open as a sign they are working properly. This is not true.

A hesitation means the engine is not making the power during that transition period so it is not optimized. Tighten the spring slightly and then take the car out for a test drive. If you can still feel a slight hesitation, just tighten the spring a very tiny bit more until the hesitation is eliminated.

The jetting for your engine will probably be pretty close for your engine at wide-open-throttle (WOT). If you want to try adjusting the primary part-throttle metering, you might look at swapping the power valve spring for a slightly weaker spring. The primary system works with a metering rod and a jet. The system is designed where a spring pushes up on a piston that is connected to the primary metering rod. Under high vacuum (low load), the engine vacuum pulls the piston downward which pushes the tapered metering rod deeper into the jet, reducing fuel flow.

Opening the throttle applies more load, engine vacuum drops and the spring begins to push up on the piston which pulls the tapered rod out of the jet which creates a larger opening to flow more fuel.

Sometimes the spring pulls the jet out too soon at light throttle and the engine runs a little bit lean. Edelbrock makes a carburetor calibration kit that offers a slightly softer spring that will hold the metering rod in the jet a little longer, which will create a leaner mixture at part throttle. This will only affect metering at part throttle. At WOT, the jetting and air-fuel mixture will be the same.

The great thing about the Edelbrock AVS2 is its annular boosters really make it a great part-throttle street carburetor. And with a little bit of tuning it can be even better!

To adjust the secondary air valve door spring, use a small Torx tool to loosen the brass locking screw. This will allow you to then move the large flat-bladed screwdriver spring load adjustment. Clockwise will tighten the spring tension while counterclockwise will loosen the adjustment. (Image/Jeff Smith)
The arrow on the left points to the spring that is located on the shaft that is adjustable. The air valve door is there to prevent a hesitation when the mechanical secondary throttle is opened at low engine speeds. (Image/Jeff Smith)
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2 Comments

  1. jens jelsgaard says:

    har en magen til på min olds 1971 350 viker godt men når motoren er godt varm og har stået stille i 15min kan den ikke starte så er den druknet og kan næsten hvad kan det være er det et stråle rør der løber
    r

  2. You realize you have the metering rod step up spring tuning backwards right?

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