serious trouble with my car cultus 2006 non efi factory fitted cng

when i start it in the morning choke works fine rpm rises but if i press race before it reaches the mid point (temp meter) rpm suddenly falls to the line above zero. engine does not stall but untill it gets fairly hot (mid point) it does tha same thing rpm rises and fall...

problem is not on petrol car is perfect...

ive tried

oil and filter change

cng kit tuning

carb and choke cleaning with carb cleaner

need help mechanic saying its advancer prob, other saying auto choke prob, other saying service kit. What to do plz advise