i have checked as you said,
1. air intake was blocked but even after removing it, the rpm did not stabilized on petrol.
2. I did not find any cut wires in the engine bay, every thing is connected through connectors.
3. yes, He did fiddled with the tappets, dont know about the setting.
4. yes, he changed the Spark plugs, dont know about the gap settings
5. As I have no idea about efi cars and the emulator or advancer used in these cars for CNG.
Can you tell me, does this advancer thing also active when car is on petrol?
if yes, then it may be the problem coz the CNG guy was saying something about its being problematic and of inferior brand. He recommended landi's original.