2 years ago I got a boat that sat for 7 years. It has a 1997 BF90. Got it to crank and idle but gas was pouring out of top carb and one fuel pump had a drip at a screw. I ended up getting all 4 carbs rebuilt, new fuel lines, filter and carbs synced by a Honda Dealer. I installed 2 fuel pumps myself. Have you checked the idle adjustment screw? I understand Honda Carbs have some tiny "jets"?? that can easily clog up. My engine has 2045 hours and runs really good since carbs were rebuilt. I also bought a Honda Shop Manual for my BF90. I will try to look in it and see what or IF it says anything about the problem you are having...my guess is the "idle jets" are clogged.