sj crash

I have a GT-15 that has been rebuilt after a crash. It starts okay but as I advance the throttle to full open it starts to surge and I see air bubbles in the line between the pump and the carburetor. The pump is new and I have triple checked the line feeding the pump from the cluck to the pump for leaks. The carburetor was not replaced because it appeared undamaged after the crash and was clean as was the insulator. I have seen a small bubble at the intake to the pump but it appeared stationary. It is mounted near inverted in a Phoenix P-47 which I am trying to get airborne once I have confidence in the engine.