So I have a 1969 Schuster Jet boat with a 327 chevy and a Jacuzzi jet. The problem is I get up to about 5mph and then no matter how much throttle I give it I go nowhere. So far I have replaced the fuel filter and taken the rope out of the pump that the pump sucked up by the previous owner. Once I did that the boat ran good for about five minutes until I let off on the throttle and now I can barely get above idle. Once I pulled it out of the water today I replaced the vacuum plugs on the carb and hoping that this will fix the issue. Does anyone possibly have any other ideas of what this might be? If the vacuum plugs don't work I'm stuck on what else to do besides a tune-up which is definetely getting done since I just bought the boat. All help is appreciated.