Used carb? A roll of the dice that it will work without a rebuild. Another vote for toomuch fuel pressure as well. A friend tuned on his Edelbrock for 6 hours one night and still couldn't get it to idle. Fuel pressure check said 7.5#. A new pump got it to 11#. A pressure regulator set to 5# and it was a different engine. A 500 horse 440 runs hard on 5#.