my experience so far with CNG kit/cylinder on my Suzuki Mehran (2004 model)
after getting kit/cylinder service,
1st filling, 8 Kg - traveled 155 km - 19 km/kg
2nd filling, 10 Kg - traveled 130 km only - 13 km/kg
went to mechanic, he serviced the kit and said to change the filling shop, but i got it filled from the same shop.
3rd filling, 5 Kg - traveled 182 Km ...........
i don't get this fluctuation.