1. Yes, have done this a lot in order to adjust idle mixture for max vacuum, here is a reading, never mind the ugly sound, it's from the air injector tube on the exhaust manifold being exposed with the air cleaner taken off.
First part is the vacuum in neutral, efter 15 seconds comes the reading in gear:
I wonder if the jumping vacuum is the cause or a result of another problem?
I have tried spraying brake cleaner on every possible leak-surface with NO change in idle speed.
2. I Have looked down the carb at idle and it looks dry from above.
If you adjust the idle mixture screws for max manifold vacuum - it will be lean.
Try adding 1/4 turn out on both screws, if this helps the idle quality add another 1/4 turn.
