throttle issue

[badluckcharm]

I have a 1999 aquatron 18ft I/O 135hp 4cyl. I Took it out today it ran fine with no issues for a while but after about 2 hrs it would seem like the throttle was getting stuck at 8-10 mph and I could push it all the way down and it wouldnt go any faster. But then when I would turn it would kick in and go. and stay there for a little but as soon as I would back off the throttle it would do it again and would stop as soon as i turned and would open up just fine and go. The engine wasnt revving high like I had it at wot either until after I turned and the boat would pick up speed. Any ideas?