I ran into a similar issue a few months back, I threw part after part at it
1)fuel pump/lines/bulb/filter
2)expensive fuel treatments
3)super expensive coil packs/wires
4) restricter/rectifier
5) hooked up a gas can with new gas/treatments
Then in a “blow up the whole motor” moment I disconnected the fuel line at the bulb, inserted the straw from my seafoam bottle into the line leaving a few inches sticking out to hook onto the can, in neutral I rev’d it to 2500-3000 rpms, and sprayed away! It actually takes a while for the seafoam to enter the carbs so if u can do it closer, maybe do that. But after I let it rest with the sea foam 15min or so, started it up and rev’d it until the white clouds stopped. Then the mercury mechanic showed up and for the life of me the boat ran perfect and I couldn’t get it to replicate this issue that plagued me for weeks, he took pity on me and checked compression/spark and all the other things and didn’t charge me much. Motors been good since. He suspects that the carbs were dirty. Today, which is about two months after that, he just called and said my carbs are on his table (upgrading to 90hp from 75hp jets) and he said that the carbs were dirty and the float needles are worn). But the seafoam seemed to work and get me by, the rebuild is just a yearly wintering thing I do.