I have a 72 with a 454. I've noticed that when I push the accelerator down to open up the secondaries in my 4 barrel carb, it feels like the car is going to shut off completely. The car usually loses power, jerks, and then sometimes starts to accelerate, or sometimes just slows until I take some pressure off the pedal to close the secondaries. If I've been driving the car for a while, say over 20 minutes, this problem sometimes goes away. But most of the time, especially within the first 10 minutes of driving, my car basically stalls when I put the pedal down too far. Any suggestions?