Not sure what you meant by starting block that you changed but in the Automatic Control Box the T5 timer has both a resistor and a diode that could be acting intermittently causing the bimetallic strip to move to quickly or slowly depending on the circumstance. What engine do you have? As the Artouste and Astazou have some different inputs to the ACB during the start sequence. If the contacts on the T5 are sticking and won't reset, you can clean them up with a fine contact file. Try changing the card in the ACB if you have a servicable spare. Good Luck!