@rizo
I have only one suggestion for you.....Keep petrol in the tank and convert to petrol if you want some fun, and return to CNG if you are going for usual drive....As you know, the engine is not a dedicated CNG engine, you will loose 10~15% of the engine's power and that is a normal thing...If still not satisfied, get the timing advanced a little bit from the distributor and you will feel a difference!