change your mechanic, if your car is running smooth and fine over petrol there is no issues, just incase some Ustaad NUThead is seriously idiot get the carb fixed from mehmood carb shop at plaza, do some thread search and you will find the map to his location.
BTW CNG consumption has very little to do with Carb at all. switch to some better workshop. There are multiple factors of high cng consumption, one being pin hole leakage in gas line which cannot be traced by ' SMELL' , 2nd most likely is retarded ignition timing resulting in Heavy Foot over throttle, if engine is laboring to gain momentum a worn out clutch etc etc.
next time when you ask a question please state the problem in detail as follows