Never set your power valve opening by idle vacuum. It was wrong when that stupid idea was first published and it's still wrong now.
If it's fat at idle, fix the idle circuit. If the power valve is making it rich at idle it's because the diaphragm is ruptured.
Set power valve opening by cruise vacuum
Why the idle vacuum is that low I have no idea. I have 10 inches of vacuum at idle and I have 255 at .050 on 340 inches.
