Big problem with psone and foreign games

[capsule]

I've a pal ps one with a mod chip installed. When I play some NTSC games (SoulBlade and Ducati world) I've a big problem. I boot the games using the boot cd, and it 's ok .
When I play in soul blade against a friend of mine, everything is ok but when I play agaist the cpu, the cpu guy stand still doing nothing!!
In ducati I can play time trial and every tpe of game when there are no cpu players, when I race against the cpu , the race does not load!
Have you some explanation,please?