Hello I'm new to the board. This is my 1st post so take it easy on me.
I bought my boat new in 2004. It is a 18' Nitro bass boat with a 150 optimax on it. Within the last year or so I've noticed about a 400 rpm and 6-7 mile per hour speed loss. I'm only able to top out at about 5100 RPM now under ideal conditions. I used to get over 5500 rpm. It's not the prop. I've recently changed plugs and when I did aside from them being carboned up it didn't look like there was anything wrong with them and they all looked the same. The motor runs smooth as can be and sounds great I just seem to have lost that real top end performance.
Could it be that my throttle position sensor is just not letting the boat reach wide open throttle? To be honest I'm not even sure how the throttle sensor and connections work.
Any help would be appreciated.