will work,wo`nt work (cdi problem)

i`m fairly new to this fix you`re own bike thing and gotta say it`s rewarding when things go right but at the minute i`m stumped!
why will a cdi which is not the correct one work and the correct ones don`t.the one that works only half works it dos`ent advance past 30-40mph but the correct ones for my bike don`t even spark?
could a crap battery cause this cause the stator seems to work fine and i know the coil to be good cause it fires on the other cdi.

Crap battery can cause all kindza problems but they are easily tested with a volt-meter. If you're sure you've got the right until then it must be that or another wiring problem.

CC