I have a 2002 Johnson 40 HP (2cyl) tiller motor that is losing power ('stuttering') mid throttle. It idles fine and runs fine at WOT. It recently became sluggish getting out of the hole, especially with a loaded boat. It stutters a bit before working through it and then runs normal full speed wide open. I replaced spark plugs/plug wires and replaced the coil because one plug post was a bit loose and had corrosion on it. Engine is run almost daily in summer time, but has always been well maintained. Could it be the power pack or another ignition component? Or perhaps another issue? 
Any advice is greatly appreciated.
Any advice is greatly appreciated.