Thanks for the replies and suggestions.

We tried my Performer RPM intake that had been used with these heads before and had the same issue, also tried another carb I used on my old 470. Still the same.

After all was said and done we discovered it wasn't a vacuum leak at all.

It was the power valves. My HP 950 came jetted square with 79 mains and 6.5 PV's. We knew 6.5 wouldn't work, we dropped them to 3.5 and that's what was in when we thought it was a vac leak.

Finally realized 3.5 wasn't low enough and installed PV block off plugs.

Ran perfect, idling right at 1000 rpm.

Now, how much to increase jetting without PV's?