When u press brake a hydraulic system is activated and like the car ac it has a vacuum device to increase acceleration, seems like the vacuum pump or its pipes are causing the problem. Because your issue is on both CNG and Petrol.
Ask mechanic to check for all vacume leaks, generally they test vacume leaks by spraying water on pipes comming in/out of engine(when water is on the pipes, it acts as a temproray glue and your vaccume leaks are filled temproraryly, ya phir ustad agar charsi ho to phir cigreate pee ky uska dhoowa pipes main dalty hy taky jaha sy vacume leak ho waha py sy smoke bahir aaye.