Also are you probably trimming the boat?

Not sure if I'm trimming boat correctly. But I took it out on Sunday used as pedometer on my phone and Speedo is correct it won't go over 35 and it won't go over 3000 RPM I have a 21 pitch prop on the boat and the motor seems to be running just fine not sure if it's throttled back don't really know

that pitch sounds about right.

More than likely you got a tune up issue. Get new plugs, wires, cap and rotors, job should be able to be done in an hour or so. Take off the flame arrestor clean it with break cleaner. Lastly check the PCV valve, take it off if it rattles your fine, otherwise replace.

Plugs wires, cap and rotor under 100 bucks.

Lastly get some fresh non ethanol gas and run some star tron or sea foam. More than like this will fix the issue

Please describe how you are trimming.

Padraig

Sounds like the motor is not putting out much power, whether because of ignition issues, fuel issues, throttle issues, whatever. Based on your description of the boat it doesn't sound like a drag issue.

Sounds like it may only be running on the primaries( have carb checked) Good Luck!!!