You can find info (you tube videos) of how to pressure test using Mity/vac 8500 or a blood pressure bulb at about 5 psi.
I use aluminum sign material about 1/8 inch thick as the plate for the carb and muffler with cut gasket material, rubber inner tube or just gasket material. It does not take much to hold 5 psi. I sometimes take the valve core out of a compression testing and inject air into the spark plug hole. Using the flat aluminum plate allows me to Spray water/soap around the edge of the block off plate to make sure it's not leaking.
The vac/pressure type Mityvac is a tool to have for several things if you are a piddler or pro and repair your own stuff, autos, small engines, checking carb needle seats just to name a few.