i know everyone heared this before but im stumpped. my big block has a healthy cam and low vac. for timming i plugged of the advance and set inital at 18 deg. at 16, 14, 12 it idles rogh. i have a petronix hei with black springs in it i get 24 deg more at 6,000. the car backfires when i rev it in park and wot after i let my foot off. i got the right springs in the edelbrock carb and i just need some advice im not going to run the vac advance canister at all forget the gas i just want the best timming set up