iv got a 83 camaro with a 72 engine, semi fresh rebuild 30 over flat tops. had just taken it apart to instal a cran cams 968821 lift 493/512. used the stock springs and rockers got it back together starts up idles fine you can slowly bring it up through the rps but if you just to rev it quick it back fires out of the carb. timing seems to be good figuring i adjusted the valves to tight i redid them still the same thing any ideas ?