[Bushwacker]

Definitely sounds like fuel starvation. When you let it idle for a few minutes, the pump refilled the float bowls, so you were able to get on plane until the fuel level in the bowls dropped. Hope you're not running premix (oil in the gas) instead of oil injection, because when you starve a pre-mix motor of gas, you're also starving it of oil! Have you checked the fuel lines between the pump and carbs? I had one of those lines deteriorate and plug one time on my old V-4. Could also be a weak fuel pump or a leak in the line to the crankcase that feeds the pulsations that drive the fuel pump!