poor performance

[jasondfree]

I have a 07 40hp 4 stroke fuel injected and cant get more than 4600rpms or more than 10mph.I have changed the fuel line from the tank to the motor (because the liner inside the line was gone) both filters and checked all fuel lines up to the injectors and no trash.I also changed the spark plugs and still having the same problem.The horn has never gone off to indicate there is a problem.Any suggetions would be appreciated.Thanks I forgot to say it runs fine on the muffs but not under a load.