Erratic timing during vacuum advance

Home from vacation and had the car out of the garage this past Sunday.
I put my vacuum gauge on the small nipple on the brake booster check valve and read almost no vacuum. I pulled the check valve from the booster, put my thumb over the inside of the check valve and the vacuum shot up to over 18"
Ten brake booster is a remanufactured booster/master unit I just bought from rock auto the past march. Rock says buy a new booster/master, install the new booster and return the leaker to them for a refund. Going to keep trouble shooting with the vacuum line to the booster plugged off until the new unit is installed.

So the motor idle slowed and had some of that nice loping that you might expect with a mild performance cam.

It seamed to run much better, but it did feel like it lost power during one series of revs to about 3000 rpm.

There isn't a huge amount of fuel in the tank so I'll add 5 gallons before the next round of diagnostics.

I didn't put the timing light on it or notice fuel pressure gauge but I certainly will this weekend.

Where should I set the timing at idle with the vacuum advance disconnected as a starting point?