Need help with this vacuum reading

Well, I agree that a fluctuation in vacuum is normal with the amount of lope it has. When I speak of locking out the distributor, I mean that you lock the centrifugal advance weights from moving by mechanically lock them to the shaft. On my car the timing would hang in there and when it started to run real rough and loose rpm you could see the timing drop by 5 degrees or more. Aside from the obvious, a vacuum leak will also make it behave this way and it would be worse when the car is warm and could also make it hard to start. Im just throwing out some ideas from my experience. Alot of things can be ruled out with a little effort and a little money. Stick with it and you will figure it out and you will learn alot along the way.