Why is Pokemon Black is lagging in my NDS? (not emulator)?

Why is Pokemon Black is lagging in my NDS? (not emulator)?

I’m using r4i v.1.4.1
The pokemon rom I’ve downloaded is from 3-4 different places, and all’s lagging
My kernel is 1.36 (the latest)

I still can’t figure out why it’s lagging so bad??? Please help me. 10 points, and I won’t forget you.