Compression readings

Put a small amount of air pressure into intake about 5 psi....Wont hold any pressure not even a few seconds.
I'm trying to visualize this ,lol
You know that there are 4 chambers connected to one side of a dualplane intake right? Two on the left and 2 on the right. I guarantee you that not all 4 intake valves will ever be closed at the same time on one leg of the dual plane. Not even two. Now I suppose you cold find the open one and back off the rockers as you did on the one, but how will you guarantee that the other three are all three also closed?