it is a false statement that the 400 Kat is Bandit based, it is not. Has no comparable bits at all.
The 250 is however a 250 bandit derived engine.
The issues with the carbs is largely that they stand for years and the they are basically GSXR flat slide carbs but the jets are so small that cleaning them can damage them.
The coils issue is just age related but also causes or joins the cdi in going on strike probably helped by the small sealed for life battery that dosen't keep charge if not kept topped up.