So I was out sailing and my usual routine is to drop the sails near my slip and motor in. So I fired the motor and it ran, but felt sluggish. I looked at the throttle and noticed it was close to full throttle, yet my speed was about 2000 RPM. I know it goes easily to 3500 and have done that in a pinch, so that was odd. I powered the motor dow and sailed a bit more. When I fired it back up (and it fired up with ease) it now seemed to only go up to maybe 1500 RPM. No warning lights or anything. So I was avoiding paddle boarders and electric boats which i the norm in the harbor this time of year and I had the motor idling. No issues at idle. When I needed to have some thrust, engine went into gear but never got over 1000 RPM. It never died or stalled and it fired right up. My biddy at the dock said he saw dark smoke and when I fired it up in the slip about 30 minutes later, it started right up but I saw a dark slick behind the boat. My initial thoughts are to check the air filter. Clogged air filter sounds like it would have those symptoms. Wont rev and black smoke from unburnt fuel. I have also read about carbon buildup in the exhaust causing it to not be able to breath. Engine has about 300 hours on it. I have had the boat 3 years and I have not changed the air filter at all. Its also due for an oil change. Ideas?