Motor will not run more than 24 mph

I have a 1983 Mercury V-6 200 Blackmax and I bought it used and the day I bought it, it ran more than 50 mph very easily. But, after that, I let it sit for about a month and took it to the lake and it would not run more than 5 mph. The next time, it would not start at all and was flooding really excessively. So, I bought 3 carb rebuild kits and took it to the lake and it would start but not run more than a minute. So, I bought a rebuild kit for the fuel pump and replaced the cone filter and gaskets with an O-ring for the cone as it did not come with check valves or I would have replaced them too. Then, it would start but smoke really heavy and would only run until the fuel in the carbs ran out and I would have to squeeze the bulb up again and repeat this over and over. I brought it home yesterday from the lake and took the fuel pump apart and made sure I had the gaskets right and replaced it as tight as I could as to not get any leakage. Today, I took it out and it ran quite well but only 24 mph. It is as though it is not getting enough fuel. I am out of ideas. Can any of you help?