Hey folks. I have a 59 with 292, mummert intake, isky cam, eddy 500 cfm carb and the original rebuilt t98 trans. Also headers with glasspacks. I have been going through lots of different carb jet and spring variations as well as timing to get the engine where I want it. I still have very low vacuum at idle. I am sure I have no leaks but with my cam I only get about 14 at idle. So anyways I have some backfiring ( not really bad ) when I am engine breaking. It never did this with other spring and jet combos. I guess my question is what would this be a symptom of? Thanks for the help.