My port engine, a 5.7 carburated motor, has trouble if I mash the throttles all the way. If I go slowly, it does pretty well up to about 4100 RPM, but then starts to lose RPM's past that down to about 3600 until I ease back off the throttle and slowly go back up to about 4000 RPM's. I've only had the boat for about a year, so I don't know when it was tuned last. I'm thinking that it is a fuel delivery problem, but I don't know. Anybody got any ideas?