Vacuum testing - expected behavior?

[ck42]

Started having the usual problems (hard brakes, delayed shutdown, etc)

So far, I've plugged every tee'd point at the end of the hard vacuum line by the brake booster so that the ONLY thing that should be drawing vacuum is the brake booster itself.

Fired it up and measured a VERY slowly climbing vacuum of about 16in. It may have gone higher but it took about 2 min already just to reach 16in.

Next, I disconnected the brake booster connection and plugged that line. I hooked up a mighty-vac and see if everything was tight and if it would actually hold vacuum. I was able to easily and quickly pull 25in. and it held rock steady.

So now, I disconnected the mightvac and reconnected the vacuum gauge and fired it up again (plugged brake booster this time). It got up to 18in. fairly quickly this time but didn't look like it was going any higher.

At this point, my info says that I should be seeing 20-23in....so I'm already low here.

Next, I reconnected the brake booster line back up and fired it up again. Again, it took a LONG time and I finally stopped the test after it reached about 16in.

My question now, is it normal for the vacuum level to take this long when the brake booster is connected? Intuitively, it seems like it might be normal since the pump has to evacuate the volume of the brake booster.

Other question is....should I REALLY be expecting to see 20-23in of vacuum or is the 18in that I was able to produce at one point normal? (or the 16in when the brake booster connected)