My 1.5 decade life at Pakwheels has passed by requesting that always mention your city or location with your posts.
There may be several reasons ranging from weak spark plugs, weak plug wires, weak coils, Carburettor issue, weak fuel pump, wiring, etc. Plus thousand of reasons.
Check and sort them one by one to reach the culprit.
If your cng is installed yet, remove cng kit, switch, filling pipe, cylinder, all it's associated wirings then go to
Iqbal Shahid Car care---if u r in Karachi
Dmotorsports - - if u r in Isb @dani_kk
Car tech--- if u r in Lahore Sadat Masood bhai