I just put my 455 engine back together and I have run it a fair amount in the garage. I have a Tri Power setup on it. All of a sudden today when I went to start the engine, gasoline started shooting out of the vent tube on the top of the back carburetor. I took off the top to verify that the needle seat was seating and that when I lifted the float and blew air with my mouth when lifted it would shut off the flow of gas. There was no evidence of foreign material in the needle seat area. I put the carb back together and it is still shooting gas out of the back vent tube. It appears to shoot gas in unison with the Fuel Pump as it pumps. The float is brass and did not appear to be heavy as if it had a hole in it. Any body had this happen to them? Any suugestions appreciated.