85 20hp surges after it warms up

[gman5.4]

my 20 wont run right for me, it starts up and runs great for just a few minutes, then it all of a sudden bogs down and starts a surging and stalling never dies just revs up and down and wont go. If I let it sit for a while(30 minutes) it will start right up and run fine... for a couple minutes.

Replaced the coils with a known good set-no help
new plugs-no help
basic carb clean-no help

What is the most likely cause? don't wanna just throw money at it. Help,please im at my wits and wallets end...

[boats.net]

Thats usually starving for fuel, check to see if primer is sucking flat if so then have a fuel restriction, try bumping choke to see if can keep it running.