For all those who own CNG Vehicles i suggest they get them tunned from ENERCON centers, as only ENERCON centers have computerized equipment for optimized tunning. Before quitting CNG for good I have used them for around 10 years and am very satisfied with the service.
here is the one I used to visit
Area: Barkat Market Garden Town
Workshop/Mechanic Name: ENERCON
Address/Directions: Situated at the PSO petrol PUMP in the service lane
Contact Details: Don't have
Specialty: CNG Tunning, KIT Service, Cylinder cleaning
Time Taken to complete a Simple Job: 2 to 3 hours for complete KIT service
Comments: ENERCON's rates are also very reasonable and they give you a months warranty. They plug a sensor into the cars exhaust, where the sensor senses the combustion and feeds a computer, thats how they how much the air -gas ratio needs to be balanced. do try them and leave a feedback.