82 Merc 40 low RPM

I recently purchased a 1991 Fisher SV18GT fully rigged aluminum bass boat. It is approx 900 lbs dry weight without the motor.
The boat is rated max 115hp.
I believe the Gas tank is 20 gallon.
I took the boat for a test ride and she runs around 25mph with two adult men but the rpm's only get up to 3200 at WOT.
The motor is a 1982 Mercury 2 cyl. 40hp. Single carb.
The prop is 11.1 dia. and 13 pitch.
Compression is 150lbs on both cylinders.
Both cylinders have fire.
No power trim but I did try different trim positions.
Checked the butterfly on the carb and it does open fully.
Water temp at test run was 54F.
I am not worried about the speed but I would like to get the rpm's where they should be.
Any suggestions would be greatly appreciated.
Thanks.

Re: 82 Merc 40 low RPM

Are you sure those RPM's and speed are correct?

25mph with a 40 sounds pretty good, although I don't know the boat.

Re: 82 Merc 40 low RPM

RPM is on the tach on the boat which originally had a 115 Merc.
The speed was checked with GPS.