Hello!
Commom Problem Boss.....Nothing To worry about..
just it need is either plug gap reduction or some better idle mixture tuneup.........
Reduce Spark Plug Gap to 0.6mm for quick start and better pickup.....
Advanced Timing to 15-16 Degrees Max with Vacuum Advanced.......better get it check by Timing Light.........
afterthat check plug wires if they need change....change them with thicker one bcz CNG needs more sptronger spark than Petrol.......Also check ignition coil....if its weak replace it with ND good one......
For best performance on CNG....Clean Air filter weekly...and set one best station for gas filling for best results.........
afterthat if some problems occur.........ask here as i am in karachi....Spectra bhai was there also....so if you need any help regarding to tuneup........i am there to help out...
b/w...margalla runs nice on CNG...good car for CNG use....
Thanxxx