21' Forester 351 ford motor

Hey guys. Having some difficulty staying on the water here's the breakdown. 351 ford dies after about 30 mins or so running as normal. I have changed the entire fuel system except the pump and tank. I have pulled the pump to check it out it was fine. The tank was opened and cleaned but I removed the check valve that was on it. Carb is a rebuilt one. It has a new coil. All the fuel lines and the filter are clear lines and I can see fuel moving along inside. If I run it in my driveway it runs forever but as soon as I put it on the water it will die after 30 mins or so I wait 5-10 mins and the cycle repeats any suggestions.

is there any crud in the tank...with the boat's motion, it can stir up crud and it will collect on the screen at the bottom of the pickup tube. Stop the engine and the crud dissipates making verifying the cause very difficult...a vacuum gauge on the suction side of the fuel pump can verify a restriction, if that is the cause.

Are you sure the engine dies from lack of fuel vs loss of spark?

I ran it today in the driveway it ran fine for about 25 mins then I put the outdrive all the way down and it died. I then put it up and it Ran again. didn't overheat

great...did the engine stop from lack of fuel or lack of spark?

I wouldnt say fuel because it started right back up. As for spark not sure. There is some sort of switch on the outdrive but I don't know what it does, looks like a limit switch. Would this be tied to the motor in some way?

most outdrives do have trim limit switches but they usually are tied into the ignition system.