Brother, you have CVT gearbox and its not suitable to use CNG on it. I have heard people saying that it destroys CVT within a few days.
You have bought it from some other person. The very first thing you should do is to change its CVT gear oil. It costs around Rs.4500/= for 4 Litres Honda Genuine Oil. Please bear in mind that only use Honda CVT Oil and buy it from Honda Spare Parts Outlet. I have seen a few other versions of CVT, one is quoted as imported from Netherlands, and other one from Thailand. Its a little cheaper but you should buy Honda Genuine.
Blinking of D means there is serious problem with CVT gear. Every good auto workshop have ECU reader for diagnostics purpose. Get it checked over there.
But I think before doing anything else, do change the gear oil and see the results if it has changed some behaviour.