2001 15hp 4 stroke rough idling problem

[dieselfumes]

I have a 15 hp 4 stroke that has a rough idling problem. I have rebuilt the carb with all brand new parts. float-needle valve - plunger - new plugs. also soaked it over night in carbureator cleaner and blew the jets out with compressed air. in aditiion I adjusted the valves. everything was done to factory specs. being a kicker on a walleye boat it takes a beating while flying down the water and the engine has always ran rough... It will idol but when increasing the rpms real slow it sputters. if I in crease the rpms fast it does repond quick. I have tried giving it more choke to see if it was a fuel problem. but it didnt change anything at all. I have rebuilt and tuned up many small and large motors before so I feel confident that I have done everthing proper. The reason why I have clear fuel line going to the carb is to see if it was sucking air. which it was. so I completly re-done the fittings on the tank ( which was brand new ) also brand new bulb and hose. one thing the bulb doesn't always stay rock hard. but it was the same with the other bulb. any ideas or suggestions are much appreciated. I have posted a video of the engine running on youtube. the sound makes the engine sounds worst than it really is. however you see and hear it sputter when I slowly increase the rpms. thanks again for any help.

2001 15 hp4 stroke mercury outboard problems - YouTube