LONG story ill try to be short. 496 bbc .585 hyd roller cam alum ported chevy heads edelbrock rpm air gap tko 600 9" 3.70 gear ran great with qf 850 carb. switched to fitech 800 mean street. new fuel tank w/400lph pump bypass regulator at 43psi. cant get it to lean out no matter what. back fire...