The vent is working properly, it is supposed to allow air in to displace fuel used in order to prevent a vacuum from forming when the engine is running using fuel.
There are great 2 stroke carb tests on YouTube by walbro that show proper testing procedures.
Basically the pressure test with a mighty vac will indicate that the needle is seating correctly. It should also hold a vacuum indicating that the check valves for the pump area are sealing correctly.
To test the main check on the portion that goes from the metering area to the Venturi you will need to use a hose and your mouth
videos are online to show this.
Make sure that the carb is wet with fuel when you do this, a dried out carb will fail every time. The seats and valves function properly only when wet with fuel.
Again these tests only indicate the above is working properly, they will not tell you if the metering arm is set correctly, or if the metering diaphragm is too stiff to work fast enough for fuel delivery.
*edit*
Btw don’t go past 10psi . Unless a service manual actually says otherwise for pop off tests etc
I’m not an expert on this at all, I just learned about these things 2 weeks ago, so I’m not sure how it damages the carb exceeding pressures.. I can imagine that you could blow out a gasket maybe?
