In short the vacuum created by the the vac pump acts on a diaphragm inside the servo which in turns multiples the braking force.

I don't know what your problem is but if you've got a vacuum leak or not enough vacuum at the servo I suspect that in the first instance you'd loose some of your braking effort. I'm not sure if this is connected in anyway to the inlet and could cause running issues.

I found this on Google which goes in to detail about how a brake servo works. It maybe of some use

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My old man wrote me a letter from prison once. It said if you don't want to end up in here, stay away from crime, women and drugs. Trouble is, that don't leave you much else to do, does it?