I didn’t read everyone’s post so someone may have covered it, but I have had 2 motors do about what you are talking about, one was a 1988 Yamaha, oil injected , unit was over oiling at certain positions on the throttle, 2nd was 1987 mercury, it would run like a scalded dog on the first run, then like you said when you go to take off again, it would bog down. Same if you idled a little while, I started have to rev the engine for a minute or 2 , to burn off excessive fuel or oil ? After that it would get up and run again . On the Yamaha I disconnected Oiler and started mixing oil in gas, the mercury I ever pin pointed it, I would just rev it up for a bit when I went to go again, pretty sure it was carburetor related though.