hie every1..

I own a vitz 2001.. Cng is already installed... but from few days my car is doing problems on cng.. sumtimes no pik and sumtimes unstable engine... got it check from a mechanic he tunned it,,, but its still doing the same... he advised me to change my advancer for problem free drive...
I need to know which is the best emulator advancer for vitz automatic...
suggestions and experience is welcum!!!
vitz owners plx reply!!

thnx...