I have a 1974 Merc 500 50 HP that I just had the fuel pump and the carbs rebuilt. I just got the boat and have never had it in the water before this so I'm not sure of how it ran before I got it. The engine Idles good but when I put it in the water when I try to apply throttle it does not gain any RPM's. The boat just sits at idle. The compression and spark are both good. The boat will speed up if I physically turn the distributor myself and engaging the carbs. I have a couple ideas but I figured instead of guessing I would actually ask for advice for once.