@all thanks for feedback.
@paindu - i had approached Honda before and they said they don't deal with CNG related issues. Later on when the problem starting coming little bit in Petrol they said to use Hi-Octane on 1:3 ratio with petrol.
But i still need to get it checked out thoroughly since it is very bad on CNG.
Btw, I got the new city model last month, few days back i experienced the drive to be less swift than usual on my way back home. I filled hi-octane in same quantity and now the drive is very swift - same as before.