suzuki outboard 1987 DT140 question

[jojo1975]

my boat is a 1984 sea nymph fish and ski aluminum 19.5feet. engine is 1987 dt140 Suzuki outboard. compression is between 117-120 on all 4 cylinder. new water pump, thermostat, head gasket. prop is a 13 by 17 pitch. came with a 15 pitch.
my problem is that I only get a top speed of 25 27 mph I think it should be getting closer to 45mph
I do not have a rpm gauge but it does not sound like its very high maybe 4000-4500rpm
it does take off like a bat out of hell it reaches 25mph in a very few seconds lots of torque whether or not I am alone or with 7 other people on board.it takes off good but max out quickly
any suggestion ????

 

[robert graham]

You really need a tachometer to verify wide open RPM's....there's one on the market called a Tiny Tach that you might use, but it would be good for all future use to have a real tachometer installed. You should be able to reach about 5500 RPM's wide open, then you can check your wide open speed with a GPS.....then a change in props may be a consideration if you're getting the 5500 RPM's and your speed is not right....