105Km/8.9Kg=11.8Km/Kg is not a good average, it should be around 14Km/Kg in local.
As far as petrol consumption is concerned, donot rely on the fuel guage readings. For more realisitc calculations you have to top-up the tank, travel for a distance and then re-top-up the tank and do the maths. If it is somewhere below 12Km/L, there is some problem.
Afterr some tunning up and change of spark plugs, the car is now giving me around 14km/kg in local on CNG.
But on petrol it is giving me less than 12 KM/L. The mechanic told me that since the car is tunned up and setup for otimum performance on CNG therefore the petrol average is not good. He says that if I need to run on petrol any time then I should remove the bush (air stopper) from the air filter and the average then would be fine. He says that the car will not give me good average on both CNG and Petrol at the same time.
Please advice if he is right.