340 Starting issue

Thanks for all the responses. This has been a 3 year project with everything new including the numbers matching motor rebuild. I had the car done and drove it down the street and back. Then it quit running and will not run. I have done the following . . .

I have power. As I said it will start and run for a few seconds then quit. Since I have driven it I know that I have power. I know that the key has 3 positions, all the way forward is start, release and it is run, then back is off.
It originally wasn't pulling fuel from the tank so I put a slight amount of air pressure in the tank and it pushed fuel up to the motor. I have a glass fuel filter so I can see the furl flow. It would keep fuel pumped up so I changed the mechanical pump and got the same thing. So I put in an electric fuel pump. I originally kept the mechanical pump and hooked the electrical to it. The car ran and drove like that until now. I switched the electric to direct to the carb and still the same issue. I thought the rebuilt carb may be the issue so I put a brand new one in it and have the same issue. It seemed that there was too much fuel so I put in an inline fuel regulator and still have the same issues. I am at a loss.