...larger idle jets. Back to the symptoms, in case anyone has similar problems. The car is a '76 GT4. Car was crackling/popping and backfiring on deceleration and the rpm wouldnt drop when I shifted. My idles were 45 and my mains were 130. The car came with a set of 135 mains and I ordered some 50 and 55 idles. I put in the 135 mains and the 55 idles and everything is cured. I understand that the original leaness was due to too small idles, but I can't figue out what caused the rpm to stay high when shifting. Go figure. If anyone is interested in some 45 and brand new 50 idles as well as some 130 mains, let me know or make an offer on some or all.