Hi @EliasK60,
I don’t know where you got the numbers for starting the 727 engines from, but they are not correct.
IRL we introduced fuel during the start cycle at 20 % N2. It would have been very difficult to even obtain 25 % N2, especially at warmer temperatures. Sometimes we could not even get to 20% N2 on real hot days in the Middle East.
Starter cutout was at 35% N2. At that point one would simply release the switch and close the black cover.