PSX backup copies

[yokese20]

I've made some copies of PSX games: Final Fantasy 9 and Tenchu 2.

The problem is that when I run the games with any emulator the CD unit begins to run, then stop, then run, then stop..... So I can't paly directly form CD and I have to make an ISO to play with epsxe, par example.

Do I have to record PSX CDs at speed lower than 4x ?

If it isn't the problem, what could be wrong with my CD copies?