Boat running a bit rough

Boat: 2007 Sanger V230 5.7 Black Scorpion engine with 125.6 hours.

Problem: It's idling at lower RPM's (600 instead of around 800) then normal, there is new smell to the exhaust (maybe unburned fuel?), and at surfing speeds (2300-2500RPM) it just feels different (almost like a car with fouled plugs)

These are just small things and the boat is still running OK, but I would like to get to the bottom of this problem(s). The differences I was noticing today are so slight that no one else caught on until I told them and they drove it.

Thanks in advance!