Fuel Issues w 1981 2001

I have a 351W in a 1981 Nautique 2001.

Only run non ethanol fuel and try to fill completely up when I store it for any length of time.
I removed the tank and slid the tank forward to replace a blower motor. Put everything back and ran on the hose just fine. Took it to the lake and ran 1\2 a tank through it with no issues at all.

When I am at wide open throttle it would begin to shudder and kill the engine like it was starving for fuel. Seems to be a lot worse when cornering or when I hit someone's wake (shakes the boat). I have replaced the water filter separator and checked the micro filter at the carb....Nothing in it.

Though that it may be a firing issue but it is not a constant issue motor will run great for several minutes and then begin acting like it is starving for fuel then shut down and take several revolutions of cranking to get it to fire back (like the carb bowls are empty or the engine is flooded). The plugs read like the engine is running lean (which would make sense I just don't know what is causing the issue. Fuel line is not kinked at the tank.

Fist off: '81 2001? Thought they were made from '82 onwards. Really early one?

About the issue: I had what sounds exactly the same problem. Started acting up in turns, later more and more in straight line too. Checked everything, replaced some stuff, turned out to be the pickup. Pull it out of the tank and clean it out. I used carb cleaner, let it set in it for the night, shake it, etc. Mine got clogged with dust and hairs and even a dead bug.
Good luck!

Anyone with Anti siphon experience? can it be bought new? techniques for cleaning?