50 hp yamaha 2002 4 stroke engine

[Brian Hoagland]

The engine starts fine. Idles fine. Goes into gear fine, and rev's up to 4500 rpm fine, problem is it slowly backs down to 2000 rpm at that point. No alarm sounds.
The carbs have been replaced, the fuel pump is new. Any ideas as to what is wrong?

 

[99yam40]

Is this while motor is under load?

Is it loosing spark to any plugs or timing retarded?

have you checked to see if buzzer works like it should