My Z has been leaking water into the #4 cylinder. I've checked pretty much everything with the exception of my block (I have 2 blocks, and I used the same head on both, and the 4th cylinder filled with water on both, so I thought it was the head. I used the same intake manifold on both, but water still leaked in). I had the idea to check my intake manfold, and I took it outside today and checked it with a water hose and air pump. When using the water hose, it didn't cause anything to spill out all over the place, but when I disconnected it and hooked it up to my air pump, dirty water spilled out all over the place. At first, I thought it might be rusty water, but it turned out to be dirt and water. Now, if the connection was plugged, could this cause the leakage that I am experiencing?

 

I'm not quite sure I'm reading your post correctly. Do you mean that the actual intake channel for cyl #4, through which an air/fuel mixture (assuming you're carbureted) is supposed to flow, was completely blocked? If so, then it's not too far fetched for that cylinder to suck in some water. The vacuum power of the intake stroke has got to go somewhere. I've heard of this before, but I've never seen it first hand, and I'd guess you'd be able to see it in terms of a minor water track past the head gasket, or something along those lines. Hope the unclogging fixes it. It sure can't hurt, at any rate!
good luck,
Dave