When I parked my car two weeks ago, it had five pounds of vacuum at idle. Today, it has zero and the gauge won't move even if you rev the motor. Checked all the usual suspects: pump is pulling, oil pan, intake, and carb gaskets are tight, gauge is holding using a hand vacuum pump, and all lines are tight. The only change that was made in the car was a new set of rocker arms and adjusting nuts. Any help solving this problem would be appreciated.

Did you clean it yet?

You had valve covers off ow about gasket there

Pan vacuum or manifold vacuum????

Pan

So what's different from before? Need to recheck valve cover gaskets, and also pump. Many times the vanes in the pump will stick if they aren't cleaned periodically. My guess is that's what happened, is vanes are stuck...

Part of the issue was the the new adjusting nut on the rockers wouldn't let the valve cover go completely down. I bought so thick gaskets and now I have half my idle vacuum back. Still not sure after tightening them down I have clearance. Pump is not supposed to need lubrication.

The pump could be pulling but a lot of times after sitting or after a few weeks of running, pull the hose off vacuum pump and spray brake clean down into it while motor is running.. Most Vacuum pumps won't pull vacuum if there is oil in there..

High/low temp/humidity changes will milk up a pump.Whether it is a 3 or 4 vane pump. A lot clean the pump and a quick shot of WD. Good to go.

Engine off, connect an HVAV Vac pump in place of your eng driven pump. Then search your engine from top to bottom and it will be talking to you.

Better yet smoke test it.

Thanks for the help. How do I do a smoke test?

One thing to consider, your leak is vacuum, smoke is a positive pressure test. Some vacuum leaks will not show up under a little pressure. Also getting “smoke” in an engine is not simple unless you have a real smoke tester.
Good luck

Check for vacuum at the pump inlet fitting!! remove the hose with the pump running...if you have strong suction at the pump....your "leak is elsewhere...If you dont have strong suction at the pump inlet.. clean the pump as has been suggested....