Vic Edelbrock Sr. began producing custom parts for cars with his design of the Slingshot Intake Manifold for a 1932 Roadster sometime after purchasing the kit car in 1938. His custom parts, including carburetors, are legendary. Tuning an Edelbrock carburetor means not having to tune it again. Once tuned, they maintain their tuning and don't need continual adjustment. They come in two styles, the Thunder Series and the Performer Series, both of which are compatible with all of the fuel mixes sold today.
Turn the two idle mixture screws (gently) all the way in until they bottom out. Back the screws out so that both screws are set at the same position, approximately two turns out. New carburetors should be set about 1 1/2 to two turns out. Always start both idle mixture screws at the same position. This pre-setting procedure is done with the engine off.
Run the engine to operating temperature until the choke is completely off and shut the engine down. Connect the vacuum gauge to read manifold pressure and connect the tachometer. Start the engine and turn the idle speed adjustment screw to adjust the idle speed to about 850 RPM or higher if the engine requires it.
Start the engine and let it run at idle. Turn one idle mixture screw 1/2 turn and observe the vacuum gauge as you do so. If the vacuum increases, turn the other idle mixture screw 1/2 turn. If the engine stumbles or vacuum pressure drops, turn the screw out 1/2 turn while observing the vacuum gauge. Readjust the idle speed screw so that the idle is maintained at the original setting of 850 RPM.
Continue to tweak the manifold vacuum pressure by adjusting the idle mixture screws. Adjust one screw, then adjust the other the same amount. After each adjustment of both screws, readjust the idle speed screw so the idle speed is maintained at 850 RPM. The goal is to obtain the highest vacuum pressure at a specific idle speed.
Balance the idle mixture adjustment settings. When one is turned out 1/2 turn, the other should be turned out half a turn. In the end, both adjustment screws will be at the same position. Turn an idle mixture screw back in exactly the same amount it was turned out if doing so caused the vacuum pressure to drop.
