get the car tuned without air blockage.
my city is tuned like that.. i dont know where the previous owner got it tuned from...
but i get excellent mileage on petrol.. although cng mileage is just a little bit bad as compared to what other city owners are getting here.
(i get 220 per cylinder on long route.. people have been getting 240-250)
and if you run your car on petrol with the air blocked for a long time.. this will cause permanent harm to your engine