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Old 01-14-2007, 04:58 PM
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Location: Cinnaminson, NJ
Cobra Make, Engine: Cobra Fibercraft Bodies 427 S/C, 351W disguised as a 427.
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MaSnaka, on a Holley carb the manifold (direct) vacuum nipple is located on the carb baseplate BELOW the throttle plates. The LARGE nipple on the base plate is used for the PCV connection. Ported vacuum nipple is located usually on the side of the primary metering block above the idle mixture adjustment screw. Another way to tell is to unplug the vacuum nipple during idle. If the idle speed drops and becomes quite rough and then smooths out when you replace the plug, that is usually a manifold vacuum nipple. Manifold vacuum at idle draws the diaphragm inside the canister forward which advances the timing (assuming that the distributer rotates counterclockwise). When manifold vacuum drops the spring inside the vacuum advance canister pushes the diaphragm away causing the advance to disappear.
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