My engine revs well in park, tries to stumble and die when in drive when I try to give it a little throttle. The primary air intake area of the carb, a Holley Truck Avenger which is new is very clean, the air intake area of the secondaries is very sooty. Have wired the choke open and vacuum secondary closed to test run it and still get the same results, plugs are very sooty too, and new plugs soon get the same color. Any ideas. 81 318, Weiand 8007 intake, Crane PowerMax cam and new lifters, new head work including the valves, all new vacuum tubing even to the canisters and new fuel lines/ hoses. Site glasses show the levels of fuel to be right at the bottom of the sight glasses. Have tried timing from 5 BTDC to 16 BTDC.