Keep in mind while tuning engine on CNG machenic usually the air intake from air filter housing plus CNG ventury also participating air intake top on carburettor , to adjust the gas air ratio , it’s as side effect they are making air intake blocking for petrol as results bad fuel average and performance, this is very wrong approach air blocking to tune cng but it’s seems mostly practicing by machenic,
Solution: remove the all blockage from air filter housing and cng pipe assembly, re tune your fuel mixture, you will have very positive impoverishment, note that keep running smooth your car on both cng and petrol , cng tuning should be performed without any jugar I mean air blocking
Good luck
