check ur ail filter box , its due to lean mixture, air box kahi se extra air le raha hai ya cng mixture set nhi kam gas de raha hai i did alot of research of spectra , its not made for cng, cng+ac p gari bilkul he beth jati hai accelerator slow dabaya karain jab first ya second gear me ho coz gari cng p ghutti hai jab aisa ho to slow slow race dain ya race kam kar dain warna backfire mary gi aur air box toot jae ga iska hal ye hai k mixture barhao cng ka aur jaha tak spark plug ka taluq hai koi farq nhi parta bosch 4 plug sirf long lasting hai nothing more aik bar dalwao phir check karna hee chordo ok aur ryte plug for spectra is bosch super 4 fr78 not fr78x, fr78x ka gap ziada hai petrol k lie sahi hai x mean 11 gape , so better buy fr78 if u run on cng coz cng k lie gap kam chahiye