I have a vacuum gauge, but haven't used it on an RX7 before. Can anyone walk me through it?

 

a vacuum gauge will only give you a hint if there is a vacuum leak, if you know exactly how much vacuum the engine normally pulls.

normally you look for leaks with a propane torch unlit or carb cleaner sprayed sparingly in exact locations.

 

Inches of vacuum in the intake plenum can be related to compression .. High vacuum is generally related to good compression in any type of engine and in that relation you can quite often tell if there is a vacuum leak .. That is the reason compression is tested with throttle wide open so it can draw all the air possible . If compression stays the same between throttle open and throttle closed there is very possibly a good size vacuum leak .

But for sure a wiff of propane will tell the story , you might want to hold a good size piece of cardboard up by the fan to stop the air movement from blowing the propane gas away .

If you are checking vacuum , each rotor should be checked via the inner runners which in turn feed front and rear rotors .. JMO . Have a good one .