1994 Mercruiser 5.7L Alpha 1 Gen II Tunderbolt

So here is the back story. Bought a boat with a cracked engine block so I was unable to run before purchase. Owner said it ran when he parked it but it was stressful because the transom filled with water due to cracked block. So I rebuilt the engine using a block I had. Everything is new! The only things that make the engine run that I have not replaced is the ignition system. Used original distributor, coil, cap, rotor, and plug wires. Now for my issue. The boat starts and runs in the drive way just fine. Get it out on the water it hesitates during acceleration slightly plains out and just about when you think you're gonna cruise it falls on its face sputters and dies. Restarts easily and then does the same thing again every time. Adjusting the timing does make it better and worse. I don't know where I should set the timing exactly to start with. In attempt to fix the problem I have replaced fuel pump, added in line electric pump, new fuel filter, and new carburetor. I've pulled the fuel tank pick up tube and that all seems fine. The only thing I haven't done yet is diagnose it by running fuel line from a gas can to the fuel pump and run the boat. I will do that and then will start attacking ignition system. Any thoughts or ideas.

Another thing I did was install a inline fuel pressure regulator with gauge. Regulated to 5 psi but while trying to cruise fuel pressure gauge would drop to zero. Same thing before and after new fuel pump, as well as inline electric pump. Don't know if this is normal while operating it.

Try setting regulator to 7-8 psi.

Most if not all mechanical and non adjustable electric fuel pumps for Carbed motors are preset to 7-8 psi. No need for a regulator.

You should not drop below 3 psi when running.

If you are going to ZERO psi then you most likely are running out of gas

You missed a restriction in the fuel line or your electric fuel pump is losing power or not working under load.