Working With the Edelbrock Performer AVS2 Carburetor
The Edelbrock Performer AVS2 is a 2-barrel carburetor designed for small-block Chevrolet V8s, Jeep V6s, and similar applications where a 4-barrel carb isn't needed or won't fit in your engine bay. It uses Edelbrock's Air Velocity System technology, which is just their way of saying the venturi design keeps air moving faster through the carb to improve low-end torque and throttle response. That matters if you're building a street engine or doing any kind of off-road work where you need power below 4000 RPM. Installation itself isn't complicated, but there are a few things most people miss the first time around. Let me walk through it.
Edelbrock Avs2 Installation Instructions
First, you're going to want to check your intake manifold and make sure the carb mounting surface is clean. Any leftover gasket material or debris will cause a vacuum leak. That's just how carbs work. I've seen too many people skip this step and spend an hour trying to dial in the idle only to find a hiss from the base. The base gaskets that come with the AVS2 are paper, not cork or rubber. Paper is fine as long as you torque the nuts to spec. Don't over-tighten. Edelbrock specifies 15 foot-pounds for the mounting nuts, which is about as much as you'd apply with a small torque wrench or by hand if you don't have one. Snug is enough. If you're cranking them down hard, you're going to crush the gasket unevenly and get leaks. Fuel line connections use standard -6 AN fittings on the inlet. If you're running a mechanical fuel pump, you need a regulator. The AVS2 is designed for about 6 to 8 PSI, and most mechanical pumps put out 10 to 14 PSI at idle. That's too much. I ran into this exact problem on a friend's 350 Chevy in a 1972 K5 Blazer rebuild. The carb would run rich at idle and stumble on hard acceleration. We swapped to an electric pump with a built-in regulator set to 7 PSI, and the problem disappeared completely.
If you're using an electric pump without a regulator, add one. It's about $20 at any parts store and saves a lot of troubleshooting headaches. The same goes for fuel pressure at altitude. If you're over 5000 feet, you might need to adjust the main jets or at least be prepared to experiment. The AVS2 comes with a jet kit that covers a range of applications, but it's not a universal solution. The choke system on the AVS2 is electric. You need to run a wire from the ignition to the choke pull-off. Without it, the choke won't open properly when the engine warms up. I once watched a guy try to drive his new build home with the choke still engaged because he forgot the wire. The engine ran like garbage until he pulled over and checked the carb. That's a 30-second fix that took him two hours to diagnose because nobody told him the electric choke needed a power source. For the secondary side, the AVS2 only has a primary venturi since it's a 2-barrel. The second barrel never opens, so you don't need to worry about secondary vacuum timing or anything like that. That's one advantage over a 4-barrel if you're running a cam with a lot of overlap. Some people assume you need to block off the secondary port, but Edelbrock designs the AVS2 to handle the unported runner naturally. The vacuum at the secondary port is minimal by design.
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Idle mixture screws are the brass ones on the front of the carb. Turn them in gently to set the baseline, then back them out. Two turns out is a good starting point for most engines. After that, start the engine and let it warm up to operating temperature. Adjust the idle speed screw until the engine idles at about 600 to 800 RPM, depending on your cam and intake. Then tweak the mixture screws one at a time until the idle is as smooth as possible. This usually takes about 10 minutes if you're patient. Power valve selection matters more than most people realize. The AVS2 comes with a 6.5 PSI power valve installed, but if you're running a cam with significant duration or a high-lift specification, you might need a higher rating. A rough rule is to add 1 PSI for every 100 degrees of duration beyond 210 at 0.050 inch lift. So a 220-degree cam might benefit from a 7.5 PSI valve. Check with Edelbrock's fitment guide or call their tech line. They're reasonable people. Heat shielding is worth considering if you're running the AVS2 on an aluminum intake manifold. The carb sits directly over the intake runners, and heat soak can cause vapor lock in warm weather or heavy traffic. I found this out the hard way during a summer track day. The engine would run fine until it hit the pits, then refuse to restart because the fuel had boiled in the lines. A heat insulator plate between the carb and intake solved the problem, though it added about half an inch of height to the setup.
If you're using a Holley or Weiand intake with tall runners, you might need a longer carb stud kit. The stock studs are fine for stock-height intakes, but anything taller than average can cause the carb to sit crooked or put stress on the gasket. I ran into this on a trick 350 build with a Performer RPM intake. The carb sat at a slight angle, and the float level was off enough to cause a rich condition at wide open throttle. Swapping to the extended stud kit fixed it. The float level on the AVS2 is not adjustable. It's set at the factory and sealed. If you suspect a float issue, the solution is usually to replace the carb or send it in for service. Don't try to bend the float tab. Edelbrock doesn't recommend it, and most people end up making things worse. I replaced a AVS2 on a Jeep Cherokee that had been running rich for months. The float was worn, and the needle seat was leaking. New carb, problem solved. Cost about $180 at the time. One thing people overlook is the venturi size. The AVS2 typically comes in two sizes: 570 CFM and 625 CFM. The 570 is better for smaller displacement engines or those with mild cams. The 625 is for larger engines or more aggressive profiles. Using the wrong size can make the engine feel sluggish or overly aggressive depending on the mismatch. A 302 with a stock cam should use the 570. A 350 with a performance cam might benefit from the 625. Check Edelbrock's recommendations for your specific application before buying.
Vacuum advance connection is on the rear port. If you're using an aftermarket distributor with vacuum advance, make sure the line is routed properly and doesn't kink or rub against hot components. A disconnected vacuum advance can cause poor idle quality and reduced fuel economy. I've seen this on a lot of rebuilt engines where the tech forgot to reconnect the vacuum line. It's an easy mistake but a frustrating one to diagnose if you don't know what to look for. Final note on tuning: the AVS2 is a decent carb for the money, but it's not going to compete with a high-end 4-barrel in terms of peak power potential. If you're building an engine for the track or racing applications above 6000 RPM, you might be better off with a 4-barrel setup. The 2-barrel design has inherent limitations in airflow capacity. For street driving, off-road use, or mild performance builds, it's a solid choice. Just be realistic about what it can do and what it can't. Edelbrock does offer a free tune-up guide with every carb, and their tech support line is staffed by people who actually know what they're talking about. Use both resources before spending money on parts you might not need.
