Kohler 13hp only running on starter fluid

This is kind of a long description of the problem, but I wanted to include details. I have a John Deere LT133 that has a Kohler 13hp OHV engine in it. My grandpa has had it since it was new in the late 90s then let it sit. He gave it to me and I've been using it for about 3 or 4 years. Recently it has been loosing power and cutting out when I'm going up a hill and the fuel tank is below the engine. It has a fuel pump and everything so it should be working. So far this year I've replaced oil, oil filter, fuel filter, spark plug, head gasket, fuel pump, all the fuel lines, got a new carb, and some new resistors to fix a charging problem. Before I got all those parts it would only start if fuel was poured into the carb and then started. That pulled fuel in from the tank. Then it started to not do that at all. It would not pick fuel up in any way. I got all those parts an it still won't stay running more than a few seconds. Does anyone know what the problem could be? It's been a reliable engine since I got it and I replaced all the parts that I listed. Thanks!

Is there an obstruction in the fuel tank?

make sure your fuel lines are hook up right onto the fuel pump.