I think I have a vacuum leak. Should the power brake booster hold vacuum when I hook a vacuum pump to it (engine off) ? I can't get it to pump up at all. ISn't that a check valave that hooks to the hose. It should allow a vauum to build correct? Thanks.

I would say you have a vacuum leak.

Buy a replacement or get yours rebuilt.

How big a vacuum pump are you using?

If it's a little hand-held job, you're gonna be there a long time trying to evacuate the big volume of the booster.

If this were me, I'd either source vacuum direct from the engine--or--if the engine didn't run, I'd pull vacuum from a different car using a very long vacuum hose. Kinda the "Jumper cable" effect.

But that's me.

How big a vacuum pump are you using?

If it's a little hand-held job, you're gonna be there a long time trying to evacuate the big volume of the booster.

If this were me, I'd either source vacuum direct from the engine--or--if the engine didn't run, I'd pull vacuum from a different car using a very long vacuum hose. Kinda the "Jumper cable" effect.

But that's me.

Its a little hand-held, but I'm not able to get any reading at all. Not even a single inch of vacuum. I pulled the check valve out and the o-ring is pretty bad. I'll replace the valve and the o-ring tonight and see what I get. Basically my symptom is that the car is not idling as well as it should be and when I adjust the mixture screws they don't seem to have much effect on engine vacuum. I've already checked the power valve, cleaned the air bleeds, checked the timing, and now I'm thinking its this vacuum leak.

Just plug off the vacuum line to the booster and see if the engine runs better.

And yes, the booster should hold a vacuum when the engine is off. You should have about two brake pedal pushes before the vacuum reserve is depleted. The rubber grommet and check valve should allow the booster to hold a vacuum. If the grommet is bad, just replace it. You can test the check valve by blocking the backside outlet with your finger and sucking on the vacuum line side, if it won't hold a vacuum just replace it.