the needle and seat in the carb adjusts the fuel level. loosen the lock screw and turn the assembly with a wrench up or down to raise or lower the fuel level in the bowl. use the sight plugs on the side to check the level in the bowl (fuel should be at bottom of hole). after each adjustment run the engine at about 1000 rpm for 30 seconds to equalize the fuel level. a high fuel level in the bowl directly corresponds to rich condition and vice versa. i had that problem in my car. if its a problem that just popped up, you might have dirt in the needle and seat or the pieces are sticking, in which case it would be worth its replacement--but beware, buy holley ones. i had problems with others.
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