440 timing pinging and popping thru exaust
A lot of folks don't consider the initial timing to be a critical spec to hold to. They try to start with plenty of initial while trying not to get to the point where the car is difficult to crank. I've always thought of a vacuum advance more as a retard system. It kicks in as soon as the motor starts so that the timing doesn't have to be set with timing that's too advanced to want to start. The problem with factory timing specs is that they rarely are accurate for a modified motor.