volvo penta 5.0 holding back from 3/4 to full throttle

by bill
(hamden,ct)

i have a glastron gs249 with a volvo penta 5.0 220hp and a carb. starts great and idles great but but when i hit it up to get on plain if i go slow it just makes it but if i hit it past 3/4 to full throttle it holds back and when i do go slow and get it on plain it will run for a bit then i can hear the engine barg down and it takes me off plain we did a full tune up cap rotor plugs wires filters and rebuilt the carb and still the same i am going out of my mind i need help thanks bill