I have a 1987 28ft bayliner cuddy cabin with a 560 Volvo penta sterndrive. It runs great no miss in motor. Reves up and sounds good in neutral. When i go out it runs fine till sbout1/2 throttle then just bogs and wont go over 2500 rpm. Had the carb rebuilt still same problem. I was told it may be the prop. Any ideas?