Yes, the air/fuel mixture screw controls your idle fuel. Did you remove it prior to soaking the carb...turning the screw in...counting the turns till
Has the carb been removed recently? Have you checked engine sync between timing advance and throttle opening. Put it in gear engine off and slowly advance
Have you ever had it on plane?
a single 5.8 in a 2755? That engine is going to have to be making 100% of it's rated power in that boat.
[QUOTEI have never heard/seen of them using Mercosil in the 15's (was definitely used in the 25's). My most recent service manual still lists the cylinders
make sure you timing is advancing...