Mike---The vacuum reading on our motors depends on several factors. A
stock motor in good shape, idling at 800rpm, with the ignition timing at
10 deg. BTDC should show up near 20 inches of vacuum.
IF that's what you once had with all cylinders pulling their fair share,
then now having only 14 inches would be very low, with only one cylinder
down in compression.
On the other hand, if you were running with a performance cam that
normally only pulls around 16 inches of vacuum, then 14 would be about
right for having one low cylinder.
Ignition advance plays a big part in the vacuum signal, at idle. It will
show up low, if the timing is retarded.
If your #4 is more than 30% lower than the others, suspect broken rings
or piston, to go with the oily plug.
Dick
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