racing alittle slow

i have a 78 camaro z with a 350 bored .60 over with 11.5 to one cr
dart iron eagle heads fully ported and polished,flame relieved pistons
cam is a .638 lift .264 duration solid roller, 4000 stall weiand team g intake, bowl's matched and blended, holley 1050 dominator carb,411 rear.
so i take it to the track and ran a 10.235 in the 1/4 i figured i would go alittle faster with dual quads so i swapped the intake to a weiand hi ram tunnel ram with dual holley dp 650's and it slowed me down to a 11.672 in the quarter.
why did i slow down with dual carbs??

dont know much about carbs and dual carb setups but did it change your mixture maybe? figure maybe changing the mixture could slow it down, dont think it would slow you down that much but thats all i can think of off the top of my head...