Patakha sound on CNG - chery QQ

[mtokeyboard]

hellow, i own chery qq 800cc with cng installed. From past 2 weeks, it sometimes gives a Patakha Sound with jhatka when car is running on CNG.
Sometimes engine also switches off when at LOW RPM on CNG specially with A/C turned on.

------------- Today i opened the AIR filter compartment to clean the filter and in the AIR PIPE that connects from AIR FILTER i found this opening (as shown in the photo). is it normal opening or is it plugged with some stopper that is not in place ?

[mtokeyboard]

FOUND IT, it connects to another air pipe tht goes to engine.

But please solve the patakha issue, is it missing on CNG ?

[meh1]

"patakha" occurs when petrol and CNG both enter combustion chamber...

[askai37]

ignition timing out

[hash4u]

check plugs condition
check the gaps
check advancer, correct working one should be installed
weak coils can cause this as well
car is backfiring. your airfilter might be burnt by now

[meh1]

check petrol shut off valve. this had happened to me in my cuore. problem occurs only on CNG so i am 99% sure.