Fuel coming out the vent pipe means only one of two things: Either the needle and seat are not stopping the fuel when the bowl fills (defective needle or seat), or the fuel pressure is greater than the needle and seat can stop. Either way, I agree that a fuel pressure regulator would be a good first place to start. I assume you set the float height correctly when you rebuilt the carb. Too high a float setting could produce the same outcome( see reason #1). Good luck!