One takes and attachs the vacuum gauge below the throttle plates of the carb or from the intake plenum.
If a stock camshaft, and fuel level set correctly, basic timing set good, vac reading should be a steady 18-20 inches of mercury, (units of a rough vacuum) in/Hg.
If a valve is sticking, leaky intake valve, mis-firing spark plug, jumpy needle between 17-19 in/Hg.
Starting vac on a cold engine, good set of piston rings, 1-2 in/Hg. As rings get older, read more miles, ie, 75K or more, this vacuum drops to 0.
Late ignition timing, late valve timing, 15-17 in/Hg, and steady reading.
Open throttle, drops closer to 0 in/Hg), thens climbs back up. If WOT, always be at 0 in/Hg.
Remember, its not vacuum sucking the fuel into the engine, its the atmospheric pressure pushing the air into the intake to fill the void created by the engine with the high pressure area created by the air rushing through the different circuits, idle and main, pulling the fuel into the air stream.
A forum community dedicated to 1st generation Chevy Camaros owners and enthusiasts. Come join the discussion about performance, builds, restoration, modifications, classifieds, troubleshooting, reviews, and more!