My buddies '70 Formula Firebird has a bored 400 with a couple of thousand miles on it. It has been completely rebuilt, Pertronix ignition, and Jett performance just did the carb. It starts OK, seems to idle OK, but when you get on it, it starts popping around 4000 RPMs. Any suggestions? How about fuel pressure, think it's running out of fuel? The pump is new but I believe that it's stock. The motor is slightly over stock but nothing too radical.