Thanks for the tips and advice. To answer some of the questions... I have an all MSD ignition system with 6AL box. I didn't change anything on the car except the mufflers. Seems to make sense that I must have been on the borderline for the fuel system capabilities and when I changed the mufflers it pushed the fuel system over the edge. Your advice seems to agree with BG and Holley as well. I'm in the process of putting on a bigger fuel pump and regulator so that I can get enough fuel volume at recommended pressure. Will probably have to check carb jetting after that. Thanks.