I don't know anything about digital ignitions,too serfistikated for me.I don't believe timing too far retarded will cause that.To backfire thru the carb usually means too far advanced timing.The spark plug is lighting the fuel mixture before the intake valve has closed completely and the flame travels all the way up the intake port and out the carb.But I wouldn't adjust the timing just yet.My car is REAL cold natured and alot of times will backfire thru the carb when first starting it.It comes from a cold intake that condenses the atomized fuel mixture back to a liquid.Then you end up with a lean-out condition that can cause small backfires.I just pump plenty of extra gas into the motor before I start it,then go real easy on the pedal.Might even try increasing the pump shot a little.Just my two cents and brief experience.Hope this helps