Won't Make Power

This is going to sound crazy for this forum, but this question is on a boat engine.

I am hoping someone can help me here!!!

I have a SBC installed in my boat. Just bought it last year and it had a problem when I bought it. Thought it was just a loose plug wire.

When I get up to about 3200RPM the engine develops a miss.
I replaced the fuel pump, carb, dist cap, rotor, plugs and wires. Even tried another ignition module with no help.

I later discovered that when this problem occurs I was loosing the #3 cylinder by shorting out the plug wires at the distributor.

I finally removed the heads and it looked as though I was ingesting coolant and thought I either had a cracked head or a bad head gasket. I replaced the head and intake manifold with Vortec style and was hoping I fixed my problem and gained a few HP.

Well this year I put the boat into the water and I have the same problem except now it looks as though I am loosing #2 cylinder!

When the problem occurs it seems like the fuel is not being sucked into the carb. There is almost a faint spray of fuel above the carb.

If I rev it in neutral a few times, open and close the throttle rapidly it will sputter out of the carb. Not backfire, just sputter.

Any ideas here? Could really use some help.

Thanks.............

Might have a worn exhaust valve lobe or lifter collapsing on an exhaust valve.

If it was a worn lobe, would it idle smooth? The vacuum readings at idle only vary between 19-20.

Is there a way I can test for this?

How can I test for a collapsing lifter?