I would like to share my experience for the tune-up of my car. I have a 2005 Civic, CNG converted. Couple of days back I couldn't find CNG at the filling stations,so i drove my car all day on petrol. The next day when I ignited the engine, it started missing when converted to CNG. An uncle of mine suggested me to go to PSO pump, barkat market and get it checked. They charged me 300 rs for the tuning, though i was concerned about getting the throttle body cleaned and adjusting the tappets which the guy there named ASIM suggested were in perfect condition. I was experiencing power loss before and the car would shift to lower gear quickly which showed power loss.
Result: Car is giving an increase of 10 km per tank on CNG and runs perfectly fine, Power increase dramatically felt. I recommend CNG vehicle owners to get their cars tuned from there( not advertising just a suggestion :))