lol, world is advancing and the mechanic recommends you to go back to 70s-80s carburetor technology.
since the trouble is without ac operations, il put my bets on the missing advancer from the whole scenario. when ac is switched on, the ecu advances ignition to some degree - no matter whether petrol or cng.
troubleshoot for any engine codes, does the check engine light come on while on petrol or cng mode?
advancer is necessary for operation on cng, no matter which car.
since you've just bought the car, i would recommend a complete diagnostic so you can get some peace of mind.
- engine compression test
- check wiring; check spark plugs/ leads/ coils
- check ALL sensors; their connections up to ecu.
- a complete engine service including engine flush (liqui moly treatment), new oil & filter (at least API-SL grade oil), new air filter, new factory recommended spark plugs with factory recommended gaps.
- complete visual check for any missing or cracked or leaking vacuum hoses or other pipes.
- make sure cng mixer area is airtight as well.
this all looks like a lot of trouble but it doesnt take long to do all this. and it will hopefully pinpoint the problem rather than blindly replacing this and that part.
efi baleno has a wonderful engine...do NOT get it carby-fied.