Why is my boat engine not reaching high RPM?

My dad bought a 1996 48 hp outboard engine for our 16 foot Carolina skiff. We took it out for the first time and the boat will get up to about 15 miles an hour. The engine doesn't sound like it is revving up that high. When we engage the choke we can hear that the RPM are really high, higher than when engine is out of neutral. We are getting a mechanic to check the engine out anyway but it would be nice to know if anyone has an idea on what is wrong with it.Why is my boat engine not reaching high RPM?
Clogged jets or an air leak in the intake system.



The current blend of fuels deteriorates old rubber parts and gaskets pretty bad.





Good luck!
Old fuel.

Incorrect mixture setting. This sounds like it is the trouble. If the engine has not been run for a while, and/or was stored with old fuel in the system, it could be caused by a partially blocked jet.

Incorrect ignition timing.

Without seeing the engine, it is hard to diagnose. From your description, it could also be fuel starvation caused by old rubber parts in the fuel supply, or again a blocked jet.

Your mechanic will probably find the exact problem fairly quickly.

Edit:
Yes, fouled plugs and/or low compression could do this too. However, if the performance improves when you pull the choke, it still sounds like a mixture or fuel starvation problem.

Don't depend on this engine until you find the problem. It could get you into trouble.Why is my boat engine not reaching high RPM?
Carbs need work.Jets are clogged.When you closed the choke you sucked more gas in the engine.

Make sure it is getting top R.P.M after repair.You can't tell by ear.
Put a smaller prop on or use it on a smaller boat.Why is my boat engine not reaching high RPM?
Before spending a lot of $ run Gumout carb cleaner in the gas tank.Also put new spark plugs and do a compression check.