7.4 TBI too rich

Hey guys, I have a 1992 7.4 TBI engine and its running too rich. My plugs are all black. I have changed the distributor, plug wires, spark plugs, MAP sensor, Coolant temperature sensor so far. I'm getting 15" vacuum off the PCV TB nipple and the MAP TB nipple. I have base timing set to 4 degrees. I get a constant 12 PSI of fuel pressure. My best guess is that I have a Vacuum leak some where. I reconnected the tan/blk wire after setting timing and watched the timing with the light and it seems to jump around but that might be because of the rough idle. Any other ideas?

Is the engine stock? If so, 15" of vacuum is low and I would look for vacuum leaks.

Yes it is stock. It kinda pops a little when you hold the rpm steady is that from over fueling?

If plugs are black, it is probably misfiring. Being low on vacuum, the ecm thinks the engine is under load and adds fuel.