Alright guys...I need some help here. My girlfriend's family has a 78 Ski Nautique with a 351 Commander in it. Here's the problem: We start it up and run it for 30-45 minutes and everything is fine. After it heats up for a while, it'll start to idle rough, and eventually sputter, and eventually die. If there is an load on it (someone skiing), When you give it gas to pull the skier up, it sputters and hesitates pretty bad. They just replaced the carb on it and have it tuned up, and her brother replaced the water intake hoses on it today. We took it out for a while, and it's doin the same thing. We tried to pull my girlfriend up and her brother gave it gas and it hesitated, and so she dropped. He left the throttle wide open and it took about 200 feet for the boat to actually catch up to where the throttle was. We've been working on it all day and can't figure out what the F the problem is. Any ideas?