yours should give you around 100-120 km in the city.. any way.. try pulling the accelerator by one hand and adjust the PEAK SCREW (silver color screw on top, that connects the pipe from the cng to the air intake) with a screw driver, keep closing it till the your car starts to stumble/resist. and open as much so you can fully rev the engine up.
Block your intake with a tape, almost 50%
Start your car and leave the engine running, if the engine is not smooth and there's alot of vibration, adjust the IDLE SCREW (Golden color, FAT Screw on the side of the CNG KIT) try to close it/open it turn by turn until your car becomes smooth.
Patience and true understanding of the engine is required in order to achieve the maximum output and minimum mileage.