I have a '56 with 312 automatic. Yrs ago someone switched car to 1957 intake and dizzy . Car has always run strong but uses a lot of fuel. Like teenage boys at a keg party!. Exhaust tips are full of black, very dry soot. In heavy slow traffic and long lights car stumbles and revs drop off due to what I suspect is excess fuel in exhaust system. Last week when this happened car back fired and quit at a stop. Huge cloud of blk soot came out of rear of right exh. manifold. What a mess.!! Engine compartment had been detailed well, till that. So...Checked float levels, rear a bit high and I reset it. Front ok. Jets were .059". I changed to smallest they make @ .049". Car runs ok...but hesitates badly till 1650 RPM +-. Installed new accelerator pump. Tried various linkage settings with no real effect. Holley book says this carb should have .053" jets out of the box... Power jet is ok. Fuel seems to dribble into carb from accelerator pump at low rpm but squirts well when throttle opens up 1/4 or more. Should I just go back to the .059" jets and live with running rich ? Timing is right on and good vacume as well. For last 2 yrs car has started immediately and has lots of power.....just a gas hog. And raw gas exhaust smell... Ideas anyone ?