15 horse evinrude full throttle problem

[helm]

My friends 15 horse evinrude was going full throttle then all of a sudden the RPMs just dropped to about one quarter speed.
Does anyone know why this would happen?
Motor runs fine and it revs up fine in neutral but when in forward gear will only go about one quarter speed.
Thanks for any help.

[Avenger]

My first guess would be a fuel problem. Does it have a primer bulb, and is that bulb going flat? If it is, it's the tank or the line. Is the tank vent open? Any water in the fuel? If not check the filter, hose connectors, etc. Possibly something got in the carb, or the float is sticking. But I'd start with the outside cheap and easy stuff first.