I'm new to boating. purchased a 1999 Bennington Pontoon with a 1999 40hp Yamaha 2 stroke oil injected motor. motor ran great until today. For some reason, the motor won't exceed 3500 RPM. Yesterday we had 6 people on the boat and were able to hit max speed which is around 5500 RPM if I remember correctly.

I have a 24 gallon built in fuel tank. Yesterday I added 10 gallons of fuel which brought us to about 3/4 full (already had some fuel in there). We went for a boat ride and motor ran great.

when we returned to dock, I added another 5 gallons of fuel because I had another full gas can on the dock. then I added some more oil so we were topped off for our next trip.

Today when we went for a boat ride we had 4 people in the boat and the motor would only reach 3,500 RPM which is about 3/4 throttle. when I went from 3/4 throttle to full throttle there was no change in speed or RPM.

Changing the trim of the motor up and down did not change the RPMs either.

Does this sound like a fuel tank vent issue? I'm assuming there is a vent that maybe isn't open?

Or is this a carburetor issue?

or prop issue? (note: I think we may have run over a log in the lake yesterday) My father in law took a "glance" at the prop and said it looked fine however, I forgot to take a look myself.

motor seems to run good and smooth but for some reason today it won't exceed 3,500 RPM.

note, I am able to rev the engine in neutral and then the RPMs got up to 5500 and could have gone higher but I stopped.

any thoughts?