There is a simple test that will confirm whether or not your inner intake gasket is leaking.
1) Hook up a vacuum gauge to the intake manifold.
2) Fully close the carburetor throttle plates by turning out the curb idle speed screw.
3) Plug the PCV valve opening (for those that have one).
4) Disconnect and plug up any vacuum hoses attached directly to the intake manifold.
5) Disconnect the battery feed wire to the ignition coil to prevent the engine from starting.
6) Crank the engine and observe the vacuum gauge. From 3" to 7" of vacuum (at a minimum of 250 cranking rpm) is normal. A defective intake manifold gasket will give, in most cases, a zero vacuum reading.
Take care,
-Chris
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