Noah, I normally go on Marine Engines Forum, just now picked up boats. My experience over the last 2 years is almost exactly yours except I have twin 1996 Honda BF40a s. Problem started with my port engine surging at higher power. I have owned them since new in 1997 and they are fresh water...
Had the same problem, under the disc is the vent for the carb. The carb is flooding. On my carb with bowl off and float and needle off the carb, I found a quite small piece of rubber on the needle valve seat. Removed and solved that problem.
