Engine Miss - I could use some help

[jasons]

I've been trying to track down an engine miss and am running out of ideas and tired of throwing money at it. I'm hoping for a little guidance.

It's your standard 350 with electronic ignition. It was running fine then one day when I went to leave work for lunch it had a miss. It stays the same if the engine is cold or warmed up.

I've replaced the gasket between the carburetor and intake which was leaking, new cap and rotor and new plugs. The plugs were only a few months old. #4 had black carbon deposits, #6 had some rust colored coating on it and the others looked normal. I have not replaced the wires yet, they were replaced last summer with the plugs and like I said, I'm tired of throwing money at it and not fixing the problem. I have checked them over and can't see anything visually wrong with them.

I did a compression check and all cylinders were at 115-125 psi.

It does have a cracked exhaust manifold on the LH side that is a recent development. Could this cause a miss?

Any ideas?

Edit: I forgot to mention that the miss is present at an idle and when under load.